Because it doesn't happen in other systems.
So, if I have a problem that only appears in one system, and not in another system... why would I assume it is a player specific problem and not a system inspired problem?
Please hear me out. There is another reason it happens in D&D - because that is what they have been trained to think when playing this game. We are all influenced by past experiences, and if their experiences are they can't do anything, then that is how they will approach the problem.
I've never denied that other people enjoy the game. But this appeal to popularity falls flat, because while large portions of the player base don't have this issue... a significant fraction of them DOES. The martial-caster divide is well known, well documented and discussed repeatedly, has been for the entire life of 5th edition and for pathfinder and beyond. Does it work for most people? Sure. But it doesn't work for everyone and I'd like it to work for more people .
I get that is what you want. But, as I stated earlier, some people think that might create other problems and then ruin it for those people it was working for.
I was just the player, so I don't have all the information. But there was an undead. I had to outdrink it with alcohol or be shot and presumably killed. It was a curse, so it likely would have at least severely hampered me even if I likely didn't die.
I told the people to get the priest, who never showed up, and my only recourse was to take the challenge. Best of seven con saves, with my monk not having good con and the undead having good con. I only won because I rolled consistently high for those five rolls.
If I had been some other class, maybe like a cleric myself, I would have had more options. As it was... I had one choice. Rely on blind luck while at a disadvantage. Both of us were stunned I made it through as easily as I did, because it was all blind luck.
So, in story terms, the protagonist in this story had to drink versus an undead. They were the underdog, and failure meant
possible death. And through an act of lady luck, our hero survived.
This is a problem? The DM has a hundred paths they can walk down that doesn't kill your character. Ones that continue the story. I will grant you, as a DM, I do not set up skill challenges that have absolutes that can end the campaign. Maybe yours does. But again, that is a DM problem.
(Side Note: For some reason your story reminds me of Sting's song from Soul Cages, about the protagonist having to drink a magical wine against the king of the ninth world, and if he remained standing, his soul could go free.

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And there it is. If you can't trust the DM, get a different DM. IF you trust DM, there should be no problem.
Okay Scott. I'm the DM. I don't always trust myself. Which DM should I go to to take my place as the DM? How do I resolve the problem of being the DM and not feeling like I have the best tools available, by leaving and looking for a new DM? Should I just quit DMing forever?
This is the FLIPPIN' problem with this argument. I'm not only making my case as a player, but as a DM, so can we stop pretending like the solution in ANYWAY looks like getting a new DM?
You're right, I did use the DM argument. But to be fair, I also asked you for an exact situation that the game put you in as DM that needed to be fixed. You came back with a character example, and even then, I can't see what needs to be fixed from a ruleset standpoint. All I see is you want your monk to be better. Not because you can't play them, but because, through poor encounter design, you had a chance to lose. So I will ask again: What specific situation have you been placed into as a DM that needed to be fixed?
Everyone was hyperbolic because of the sheer number of people in this thread who keep insisting there is no problem. I'm sure about half the people in this thread say there IS a problem. And that should say a lot too. Except you'll dismiss them, because they aren't talking about the "real" problem, which is the player, or the DM, or anything that isn't the system.
Again, I have not dismissed anyone. I have asked for examples. I have received very few. Most just say this martial/wizard thing is a problem, so let's make the martial stronger. That, in my opinion, just sounds like half the arguments on these forums: I want my character to be able to do this, and they can't. Therefore, we should change the rules/add powers/etc.
Um... am I missing something about the Androsphinx here? It has nothing that prevents a caster from wrecking it.
Also, a 20th level wizard can absolutely wreck a CR 15 plus minions? Again, what the heck are you talking about here? That is almost trivially easy for them.
We must not play the same game. Because the androsphynx would present such a challenge that the wizard might have a 50/50 chance. Not good odds for someone who has spent years playing a character to get them up to this level. I should add, that is without any DM shenanigans as well. Throw in those, and the odds shift to 90/10 in favor of the androsphynx.
But frankly, I'm convinced it is the system. Sorry about it but after 100 pages of discussion, yet again, I still don't see anything being proposed that somehow changes anything. This isn't something that has only been discussed this once, or just on this site, it is EVERYWHERE, and the consensus seems to be that the gap exists. So let's fix it.
To prove I am not being dismissive, I have laid out options (maybe three) on how to balance the game better for those that see a problem. That's with me not even seeing the problem. I have talked about tiering the system and its flavor text (I think words, even flavor words, matter). I have suggested that martials not be bound by the 20 cap on abilities and allow them to raise to 30, while casters remain at 18 or 20. And another way to solve the issue is to limit spells by adhering to components, finding the spell, or simply removing the one or two that seem "breaking."
I have proposed all these things in this discussion. None of them work for people because they want their martials to have more. It's a never ending cycle.