Schools do not want these non-school teams coming in and trashing the joint on Saturday afternoon, right before their big game on Saturday night.
My bet is that they would charge the league, and the league doesn't want to risk having to pay for damage, hence the league makes a tough rule. It works for me!
Then again, I like Denny Bridges, the former Illinois Wesleyan coach (most famous alum was Jack Sikma of the world champion SUPERsonics). Upon his recent retirement after an unbelievable number of years coaching at IWU, he just finished a book titled "A Dunk is Only Worth Two Points." It's on my birthday list! (if you wanna get it for me, I'll be happy to give you my address
)