You know, I guess it's because I do 50 mile rides just "riding," and I've done a few metrics either on my own or with my club. The one century I did had like a $30.00 registration fee, which went to the club that sponsors the ride. I feel like I don't need the structure to "train" and do that kind of ride, nor do i necessarily do those rides at my fastest speed. So, if I am going to do charity ride, it would be because I really believe in the cause... because I am going to be riding anyway.
I've heard some negative things about TNT, at least around here. It's "faster, harder, train more," etc., which would certainly turn someone like me off, because I generally ride these kinds of rides to "finish," although I am usually not last, either.