You've drastically overstated the number of students from UO who were there. The US Forest Service estimates that there were 1k people there on the weekend in question, not all of whom were from the UO.

None of this is to say that the actions of the UO students in attendance weren't deplorable in the extreme. But the conclusions you draw from your bad data are patently absurd. Colleges from all over the region go to Shasta for exactly these kind of parties—though most of them evidently clean up a little better. There wouldn't be an enrollment crisis if UO told Greeks (roughly 10% of UO's student body, a small proportion compared to, say UW) that they couldn't trash Shasta next year.