I agree with Jetmech on this one. In fact, the way the thread is titled is a little too authoritative. People may have their own private reasons for this that they do not wish to share or have to "explain themselves". Now I will try to explain some possible reasoning without stepping on any toes.
********PLEASE NOTE, THIS IS NOT A NEGATIVE COMMENT TOWARD SUB-TEAMS OR BORGERS**********
First of all, I commend the borgers for their awesome ability to collect folding rigs like baseball cards. I also commend the sub-teams for bringing in folders that would not normally be folding. Now on to my theory. I believe some of the people listed are folding for other teams. The primary reason most of us fold is because we believe it is a worthy cause. But, we still enjoy seeing our names move up the ranks. With the recent increase in sub-teams and borging, we are moving down the charts. We don't want to be on a subteam (I'm already folding for a team yet I still can maintain a portion of my individuality) and we don't have the opportunity to borge rigs. We fold only on the computers we build. Thus we no longer get the pleasure of seeing our names move up the charts. We don't want to quit folding so we seek out another team where we can again enjoy the pleasure of watching our increase in the ranks. We are still dedicated to the folding cause, but we just don't enjoy moving down. Personally, I have moved from the top 100 to dangling around the 120 area. I have considered finding another team, but when I look around, I haven't found a home that fits quite as well as this one. I've accepted a new attitude toward this myself. My goals are now points and not position. If I ever get the opportunity to borge, I'll jump on it and then maybe I'll move up. Until then slow and steady like the tortouise.