i don't know about other people, but whenever i play a game that really feels special, i procrastinate finishing it because i'm afraid i won't want to keep playing it when i'm done, so i just dick around and do side quests and collectibles, then a couple hundred hours later i'm sick of the gameplay and i just never finish the game. it seems to happen more with games that really immerse me than shallower games i don't get as attached to.
i'm working on it, but it's a habit i've noticed.

as for the difference between platforms, i assume steam sales are a factor, no idea why playstation and xbox are so different.