Obvious reasons: locking young people in universities in their highest testosterone years reduces crime and drug addiction. Especially among people who don't get to have much returns from that education.
But I think the modern equivalent is closer to high school, because we have a society that places inherent value on universal grade school education, and thus mandates attendance (anti-truancy, etc). One unfortunate effect is that for some, school ends up feeling like a prison or holding pen just to keep some young people off the street and out of trouble.
this could very well be true, but it hardly seems obvious. i could readily believe that fewer serious crimes occur at universities, but it seems like the combination of a large, low-friction network and a general blunting of consequences would lead to more drug use at least, and the ability to avoid or defer direct consequences does tend to exacerbate addictions and increase their harm over time.
General crime maybe...drugs not so much.
Considering how safe I'd feel on a college campus at 2am on a Friday night compared to a rundown section of town, I'm tempted to believe that college does keep kids away from the worst of violent crime. I can't find any studies on the subject, unfortunately.