I’ve had a student install a super cheap (g only) repeater to provide wifi to their car in the car park, due to its location a number of students ended up using that rather than our APs. This slowed access for them dramatically.
I’ve had a student physically remove an AP to get to the 2.5 gigabit port they connect to, they somehow thought that would be better than the 1G they have in their rooms, despite it all being the same link out.
An overseas student cloned a MAC of their device to a travel router and effectively ran a VPN server for their family to try and give them an IP in our country.
The accommodation only has an hour of my time per week or so, they’re not paying a lot so issues only get dealt with when I have the time for them, this leads to an extended period of bad access for folks and many complaints to the staff.
The main point of the story is that not all students take the experience of their neighbors into account. Hence the restrictions.