RE: Why did you join the AMA?
The proper chain of events is that if a club wants an AMA Charter, then the AMA requires that all their members also join the AMA. If a club does not wish to be an AMA chartered club, then there is no requirement to join the AMA. So the rationale is that if you want to enjoy the benefits of membership, then the AMA wants you to be a member. One primary benefit is that the AMA provides clubs with site owner insurance making it easier for clubs to obtain flying sites. But as has been made clear in another thread, some clubs can get their own insurance and therefore AMA membership is not required.
Another benefit of membership is the ability to compete in AMA sanctioned contests and events. Again, in order to do so the AMA requires that you be a member.
I just fail to see what the big deal is.