For some reason as soon as I get to the “end” of the game, I completely lose motivation to play. This happened with DOOM: Eternal, Sekiro, Bloodborne, Paper Mario TTYD, Cassette Beasts, Shovel Knight, Oblivion, Baldur’s Gate, God of War, Mass Effect… Pretty much every game I’ve ever played. It’s like the fun part was the journey, and I’ve seen everything the game has to offer, and I just don’t really enjoy the ending process. Feels like a formality at that point.
It depends on the game and the difficulty spike. I know what I’m getting into with a FromSoftware game, and they’re usually reasonable progressions (outside of some the DLC bosses). I know they’re tough, but they should be manageable with some adjustments and patience.
Then there’s games like TTYD that shot up the difficulty at the end without much warning. If a game just throws a curve ball like that without much of a means to build you up for that fight, I think that’s a failure on the game’s design.