The best answer I've heard to that question, which I've asked also, is that contests appeal to ops with limited operating time. This is particularly understandable given complex family obligations (kids, school, relatives) and work obligations (projects, biz trips) where things have to be planned out weeks or months in advance. There would never be time to get on the air casually, but it works if there's a specific event that can be put on a calendar. Not the reason for everyone, but worth mentioning. Of course there's always the competitive aspect. Ragchews are not challenging to those who thrive on competition.