The GM thinks the players will enjoy it.If the conclusion is foregone, why are we engaging the mechanics?
Usually to give the illusion that this is not so? Just a guess.If the conclusion is foregone, why are we engaging the mechanics?
Because the real treasure was not in the destination but the enemies we made along the way?If the conclusion is foregone, why are we engaging the mechanics?
The GM thinks the players will enjoy it.
Seems as though these are both in the range of correct--and I don't even see an inherent conflict between them.Usually to give the illusion that this is not so? Just a guess.
I've run Mothership, which is heavily inspired by the Alien franchise. There are rules for getting new PCs mid-session. Players go into it knowing that they aren't adventurers in balanced fights. There are the dead, martyrs, and survivors.
I've played Call of Cthulhu, where getting into a fight in the first place is often a lose condition, even if you are the "winner".
I've player and run non-level specific D&D over multiple editions, which the players know about going in, so analyze foes instead of just assuming if they can fight it that it's a balanced encounter. That prepare to retreat. That the DM trains the players not every encounter is on-level, telegraphs foe strength when appropriate, and at least early on will give foes reasons not to pursue (mother bear defending cubs, ogres in an area with kobold-sized caves the players can squeeze into, etc.)
Yeah, I see how a "non-winnable fight" could get under the hackles of players who have only been exposed to balanced-encounter-only D&D. And frankly many (most?) DMs train their players only to expect winnable fights regardless if it's homebrew or a module, with the occasional "you're not anywhere near the right level" of someone like Strahd.
And a non-avoidable, non-retreatable fight often (but not always) is a red flag about GMing. Though even "non-avoidable" might be avoidable based on earlier choices. For instance I was playing in an Theros/Ancient Greek themed D&D 5e game where we knew there was a red dragon on the island. We spent several days in the (slaughtered by raiders) village because our boat needed repairs and instead of doing the minimum for a sea voyage and getting out of there we got greedy and instead were repairing a better boat of the ex-villagers that had been hulled, and bringing over ballista from a third boat. Sure enough, one evening the dragon paid us a visit. Once engaged there was no way to avoid the flying dragon which ended up burning down the whole village. Even those hiding under the waves eventually came up for air. But could we have avoided it? Sure, but repairing our boat and getting the heck out of there.
Side note, it ended up in a TPK, that immediately turned into plot because of what we had been doing, and a chance to give up our earned eternal resting spots (differing based on our deeds) for a chance to escape the the underworld. So even in that case the DM made it work.
To sum up, once you start going outside traditional wargame-inspired boundaries, fights that you just shouldn't start, or once you've engaged you need to look for alternate win conditions or just retreat, aren't such blue moon events. And when they do show, they can be made to serve the story everyone is crafting together.
I'm not sure "unavoidable defeat" is a problem exclusively in (or inherent to) any edition of any game--but I'll agree that it happening on streamed play shows (which have some important differences from play at most tables) is connected to how a lot of people are playing now.I think that a lot of times, yes, it's a D&D problem. One that is especially exacerbated by the messaging of the current edition and the published campaigns.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.