A lot of the games I play only once or twice are "cute" and "fun" the first one or two times, then get very ... predictable. And naturally some are just games I don't like at all. I play them once, then never pull them off the shelf again.
Some games I really like, even after multiple plays, but they're too much a chore to set up. Or they're too hard to get the right number of players together for. Or they take more time than I usually have. Or they take more space than I can spare.
Then there's the "new shiny" problem. I could play some games over and over and over again, but the people I'd play with have seen this new game and they want to try it. And so many board games are being published weekly (it seems) that there's ALWAYS a new shiny that keeps people running toward them.