Oh, so now you just want to think that all the PC deaths are my fault because I happen to be DMing? Wrong. I'm not saying I haven't done it in the past -- my first 5E encounter was misjudged as I didn't understand the balance and was comparing it to AD&D. A critical hit caused a PC to die in the first round. Not the player's poor choice at all, my bad for miscalculating and my inexperience. I apologized to the players, we had a bit of a laugh, and after they managed to win the fight (barely), the curate was able to raise the deceased PC. Since then, it never happened again.
The anger I'm reading in your post right now? The "Oh, so now it is MY fault". That's what I've been getting from your choice to say it is the player's "poor decisions" that lead to their death.
You want to say that "poor decisions" and "miscalculating" are equivalent statements, but they aren't. "Poor decisions" carries with it much more negative conotations, including the implicit "and they should know better" part of it. I've never seen someone say "Oh, they've miscalculated their life" but I have certainly met and known people of whom it is said "they make poor life decisions"
Honestly? I don't think PC death is anyone's fault, except in the most egregious of circumstances. The DM has an incomplete picture of what they think the party will do and what they are capable of, the party has an incomplete picture of the challenges the DM has arranged and what they can do, and then the dice throw everything into the blender. Sometimes it works out okay, sometimes it works out great, and sometimes the PCs are making death saves and everyone is thinking "what the heck just went wrong?!"
And I know you've added the caveat of it possibly being luck, but you've also doubled down again and again and again that it is usually because of the PCs "poor decisions" and every time I read that, I get "The PCs made poor decisions. They should know better, and if they had made better decisions, this wouldn't have happened." But unless player's are actively acting up, they aren't making plans that they think are poor plans. They think the plan will work, that's why they made the plan.
And I brought up you being the DM, because I have often found for myself, that I forget how much additional information I know compared to my players. It is very easy to watch a player do something that I think is obviously dumb, then realize that I think it is obviously dumb because I know something the player has no knowledge of. It is much harder to appreciate a plan that relies on a lack of knowledge that you do not lack.
I'll give you two more examples, the last times I've seen PC deaths...
1. About a month ago in my new Monday night group. Since these are new players I was letting them make the decisions and drive the story. They had us split up into two groups (1st poor choice, as I just shook my head...) to search some buildings. One group of 2 and another of 3 PCs. The DM was running the 2-party group first, and they met two cultists and defeated them, but one PC was injured. Then the first zombie came. They PCs yelled for help and the rest of us came running, luckily we weren't that far away yet. Our DM admittedly is rather new, but fighting zombies isn't too bad, of course, but we're 1st-level, so not necessarily a cakewalk, either.
The injured PC, instead of being defensive and waiting for help to arrive, decided to attack (2nd). He was hit again and went down. Meanwhile, his companion was fighting a 2nd zombie which just joined.
Next round the rest of us arrived and engage the zombies. We healed the downed PC, but he was hit again and went back down (darn whack-a-mole!) because (again) he didn't dodge when he got up on his turn (3rd). Anyway, we then destroyed the first zombie, which exploded in a ball of acid spray! The DM has us all roll DEX saves, some made it, some failed. BUT the "bad luck" was the DM's "custom" zombies exploded for 4d6 acid damage (4th) and he rolled 23 points! Yikes, right? But even if he had rolled average 14 damage, it would drop any who failed their save, and even some who made it (like our 7 HP sorcerer...).
Obviously exploding-acid-zombies dealing 4d6 damage vs. 1st-level PCs is a miscalculation on the DM's part, which led to a TPK. My PC was the only one who went to 0 hp after making my save, the rest died outright (some due to low hp, others due to being injured). But even if they had been at full HP, none of them would have been conscious, regardless.
So, the ultimate issue was the DM's miscalculation.
On your Second "mistake", do you think it was a mistake to attack the Zombie because you know a 22 hp Zombie can't be taken out by a 1st level character's single attack. Unlike the only other creature this player had ever fought, a 9 hp Cultist?
If you assume that the PC thought they could take out the zombie in a single attack, does their plan still seem so terrible?
For the third "poor decision", this was a new player. Did he know that Dodging was an action he could take? I'm assuming he attacked again instead of dodging, perhaps still thinking that he was dealing with a threat he could take out. I'm also assuming that he was a front-line character like a fighter or barbarian, and so likely he was told at some point during character creation that his literal job was to get on the front-line, attack, and take attacks. Could that have played into him getting on the front-line, attacking, and not dodging in the back line instead?
And frankly, it seems like splitting the party did nothing, and the entire thing was predicated on those exploding zombies. But can you see how the player who kept getting up and attacking might not have seen their actions as "poor planning?"
2. Two weeks later I was running a game with the same group. 3rd-level this time. They were given clues this was a dangerous area! On entering a maze, two scouts working in tandem to keep an eye on each other (they were learning, unfortunately not enough). The first was invisible due to a spell cast by another PC. The second was following by holding a rope, which the first also held. Two other PCs were keeping watch at the maze entrance, also watching the second scout. A short way in, a minotaur appeared and, moving toward the second scout, literally ran into the first since it occupied the space it needed to pass through. Sensing something might be there, the minotaur attacked with reckless attack and hit, dealing 2d12+4 damage, which is A LOT for a 3rd-level PC!
They realized they needed to run, but as the second one moved back he saw a 2nd minotaur and rushed at it to attack (1st poor choice) it to prevent it from blocking their retreat. He could have fled, knowing his still invisible ally would be able to run without an OA since he was invisible. They both could have made it out.
Hearing the fight, the other two went in to help. I'm not going to go into the full play-by-play, but after getting hit the second scout didn't defend themselves (dodge) to wait for the help, but insisted on attacking. The critical hit which landed next resulted instant death. If the PC had dodged, it most likely would not have been a hit, let along a critical hit.
By being overly aggressive, not thinking about defense, etc. that second scout ended up dying. Even if the hit hadn't been critical, it would have likely dropped the scouting PC.
Again, these are new players, but were warned this area was dangerous. They realized the danger but the one player decided to engage a much more powerful foe instead of retreating to the others. The invisible scout would have been able to flee before the second minotaur cut him off, or could have snuck by / tumbled past to escape. There might have been issues with it, but we'll never know.
In conclusion, can bad rolls contribute to a PC's death? Of course! But for a player to claim it was just bad luck IME is often wrong. Poor choices contribute to PC death more than the dice rolls.
So, still new players, only two weeks of experience in the game. And your 1st "poor decision" is a tactical choice to hold off a monster so the others can escape, which is poor because the new player, likely dealing with a new spell, "knew" that invisible creature's can't be hit by opportunity attacks? Man, I've been playing with people for years and we STILL sometimes forget that.
Also, Minotaurs are CR 3... as in a single group of 4 adventures (what is sounds like you are dealing with) should be able to take 1 of them. We have two, and they ambushed the party while the party was invisibly scouting the maze. That's basically a deadly encounter right there.
Also, you are really a big fan of dodging, but Minotaurs have 75 hp, a 3rd level character is likely dealing 7 damage a round. In other words, they have to land at least twenty hits to stand a chance. If the PC started dodging and didn't stop for multiple rounds of combat, they would have just died slower. Especially since he had JUST seen that disadvantage on attacks didn't stop his friend from being smashed by these things, since invisibility didn't help. Of course, they also don't KNOW how much health the enemy had, and were maybe hoping they could kill it before they got smashed to paste.
Also, yeah, they were told the area was dangerous. But "this area is dangerous" and "You can't survive two attacks from these enemies" are VASTLY different things. Yes, clearly from our perspective it is obvious they should have run. But they'd played what? Three sessions total? They didn't have any context to know that this was basically an unwinnable death trap and their only option was to flee. If this is your best example of character death being because of "poor decisions" from the players... man, I don't know. I'd say sending two minotaurs after four newbie players is incredibly harsh. A single minotaur would likely have dropped most if not the entire party at that level. And would have been a far better way to indicate to them to avoid that area like the plague.
Seriously, if I had been the DM, I would have been much heavier handed in telling the players that running was their only option, because there was no way to win that fight.