In my case, it's not so much feeling like I need to play certain games.
I'm the kind of guy that, if I'm not having fun with a game, I drop it, with no hesitation.
It's more a case of:
I'm having a blast with a certain game. A new game comes out that I really want to play, and I start playing it. Before I know it, I went a couple of months without playing that first game, and now I have to drop it, since I no longer remember what is happening with it, story-wise.
Then, a new game comes out that I really want to try, and I end up doing the same for that second game.
Repeat, and you get a lot of unfinished games (that I want to replay or finish), on top of all the ones I never even started playing (that I bought, with the obvious intention of playing).
I used to love playing long RPGs, it was always my favourite genre, but now, I'm more likely to play either games I can just pick up and play, without a plot (pinball games, or shmups, for example), or short, 2-4 hour games.