Is this just me who suffers from this?

A few of my mates who go to uni in London and have done for over a year NEVER seem to bring their Uni mates out to things with their old friend "groups" or invite me (and other old friends) to anything involving uni pals.

I mean, I understand wanting to socialise with different groups of people from time to time, but if it bothers them that much why stay living at home and not live in halls in I dunno...Wales or whatever where you can have Uni friends and home friends?

I just find it odd.