Yeah I always thought this was a reasonably big difference with the US. What if you don't get along with your roommate? I'm all for communal living as a student, but you need some kind of space that's only yours, even if it's quite small.

Btw some of the London unis do make people share. At least one friend plus my wife were having to share. Drives people nuts, especially if the other person has some issue like snoring or excessive partying.