Because perhaps the other people considered last time haven't applied. In fact I seem to recall that most of the people considered last time didn't want it then either, it was just the regulars saying they'd be good. Regardless of what some people may think, it's not a popularity contest, and again, as Baelorn says, personality doesn't even really come into it for the most part.
For instance, I'm quite confident that I could do the job quite well regardless of the fact that many people dislike me. However, I don't want it because A: I'd have to spend a lot more time here than I really should be with my school and B: I'd have to stop trolling people.