damasa, it's difficult to respond to that without getting into a local vs. national debate... But here goes
Forcing national groups to go local could be exactly contrary to the aims and desires of these Universities. While national organizations do actually excercise some control and restraint, have well thought out risk reduction strategies (that are supposed to be followed) and actually have their own oversight... Locals aren't required to do this. This leaves the University with the choice of not recognizing them (ie. getting slapped with discrimination lawsuits if they're public funded schools) or recognizing them and running the risk of being named in future lawsuits.
The umbrella of national organizations really should be attractive to Universities. I'm not saying that locals don't do these things, they are just not required to. I think it stems mostly from incorrect perceptions by administration as well as backlash from the overly PC community. How dare we have exclusive groups!