I would have to read our constitution to be 100% sure on this; however, I think you can only run for a certain position twice...like the President of the US, you can only be president for two terms, and than you have to move on. What happens in the sorority world is that those same people sometimes run for other sc positions.
Also I've heard that not many of our sisters are up for the challenge of being a sc member...its all volunteer work and alot of time with conference calls, constant emails, and constant travelling. It might be tough to balance it all when you have other things in your life as well.
Also, many of our sisters feel like the could do more working on the local level rather than the Inter-national.

Maybe when I retire at 40 I'll take a stab at it.