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.
I had this with Metroid Prime 4 just the other day. Have seen what I wanted and then got to the final boss. I didn’t have absolutely every single upgrade so the boss was probably more annoying that should be.
After a few goes and some bullshit deaths I just put it down and sold the game. I felt I was done.