There are simply people who want to participate more than they want to win. I mean I personally don't really understand that way of thinking (as someone who died and then PM'd my teammate quotes from throughout the game to try to help him win) but I guess you can't really blame people for just wanting to play as long as possible.
You are right, it is tough to blame them. That said I always play to meet my win condition. If I think speaking up and getting killed at night because of it will help the town, I will do it. I just think playing dumb hurts the town more than it helps. In any case everyone has the right to play the way they want to play but I can still be an ass and complain about it haha.