Why does anime always do that thing where it seems like somebody is going to break their moral code/disobey orders/disappoint their sensei/some other thing, and there's literally minutes of buildup until they pull the trigger, then at the extreme last second all their motivation disappears and it turns out they were never really going to do it all along? It's a crappy twist, and it's very annoying to suddenly have the entire conflict of the episode/movie/series/etc. just disappear like it was nothing. Like if, in the last thirty seconds of Revenge of the Sith, Anakin just kills the emperor and says "lol i was really jedi whol tiem!"
You say that as if, canon aside, it wouldn't have been a better ending to the prequels.
Like dude, Palpatine is obviously evil.
Edit: Not arguing with your point on anime, just saying if you take the prequels in a vacuum Anakin turning evil is the more contrived option. Like yes he was a terrible jedi and grown-up Ani should have been expelled from the order halfway through the first movie he's in. But there's a difference between "bad jedi" and "ruins everything ever for the sake of a plan that obviously isn't going to work".
Sith was a prequel, which constrained how they told that. It's not indicative of normal Hollywood endings. I got sick of Hollywood because of all the tacked-on "lol we're all ok after all" endings, which you actually see less of in anime. What you
do see is more cop-outs in arcs that are not the final arc in manga/anime, but
less cop-outs in the actual story ending.
As for why a serialized medium would have a lot of backtracking on ideas? It's no different to The Simpsons resetting every episode, except less frequently. People generally expect a story to stay in the same genre. Big story changes threaten the ability to deliver that. E.g. if you pick up One Piece in shonen jump, you expect it to still be about Luffy and his pirate crew, even years later. Bad guys might threaten to destroy the ship, but there's always some twist to stop it happen. If you've ever read or watched a series where there was a long arc in which they did something that's not in the core story's genre, you probably know that these sections tend to drag out and you're like "wtf when are they getting back to the <type of stuff this story is known for>". If that was a
permanent change because "it's a consistent plot development" you'd alienate your readers en masse.
The "big threats" are needed to keep the story rolling, but they're never carried through. The real "Big Threat" is anything that would derail the story right out of the genre it's in. A main character permanently losing the powers which the series is about is way too far outside the genre: it can't happen, and you still have a story that makes sense to continue. But the powers need to be under threat rather than just given, because that prevents a Mary Sue feeling.