The main difference in colleges is nobody is forced to be there, you don’t have rules about when you’re allowed or not allowed to be in the hallways, and they generally treat you like an adult. You don’t have to get a hall pass to use the restroom. Rarely do they take attendance. And I’ve never been in a college with locking grates across the hallways.
Generally the students at colleges are adults, which might explain that...
A lot of the rules in public schools result because parents expect the schools to be responsible for their minor children at all times, and if said minor children choose to be in the wrong place and get hurt, etc., the parents can and do hold the schools responsible.
Rarely do they take attendance.
They didn't when I was an undergrad, and most of my graduate professors didn't, but judging by the syllabi I've seen from my youngest child's college classes (which isn't all of them by any means) more and more college professors are taking attendance. I'm not sure why that is.
When I was in college, most of the professors didn't take attendance because if you weren't in class you weren't going to pass anyway. The ones who took attendance were the same ones who basically read the textbook to us in class...a certain economics professor comes to mind...