In highschool you were mostly going to school with the same kids since Elementary school, and there was probably such a limited amount of things to do academically and socially, that most people fall into one big group or a bunch of smaller groups that just merge at parties/dances/kick-backs etc...
In College, everyone is probably into their own thing and you just have to actively seek out people with similar interests. Check bulletin boards, postings, listings etc...for clubs/groups/social gatherings that seem interesting, a lot of times you might meet the best people via friends of friends of friends etc....you never know.