In addition to the normal logistical stuff that’s always a problem (finding a group of people who all want to play together, play the same game, can get together at the appropriate time, etc.) I think I’ve noticed a “social proof” thing where I have trouble staying enthusiastic about a game if I don’t feel like other people are playing it (I’ve noticed something similar with video games, too). Intellectually I think it shouldn’t really matter, whether the game is fun at the table should really be the determining factor, but based on observing my own patterns of behavior I think there’s something about energy and buzz or the lack thereof that has some effect on my motivation to play a game.