as i remember there were a number of reasons

1) responding to requests of other club members
2) booking friends. you don't always like the music your friend plays
3) maybe you owe a favour to another club organiser - so you book an act, because the act will visit your area for two bookings but not for one
4) admiration for the skill of an artist - even if its not really your sort of thing
5) a cracking review that makes an artist of interest

probably hundreds more reasons, but what else would you do?