You are kidding right? Any fast food restarant owner would kill to have those kinds of crowds at 12:30 at night. I can see the k-mart wanting to get rid of them and perhaps the other business's which were all probably closed at that hour. So they were not driving away customers but may have been worried about vandalism. That was definately not true of the Sonic drive in.
Actually, they don't want them: they don't buy food in proportion to their numbers, and they tend to drive away the paying customers.
If I'm thinking of hitting the local Sonic or Wendy's, and I see a bunch of teenagers milling around in the lot, I pass it up. That many kids doing nothing at 12:30 AM can turn into a bunch of kids engaging in vandalism or fighting for no discernable reason.