>The reason that college works in forming friendships and romantic relationships is the artificial environment it creates where people are obligated to show up and mingle with people who are from different backgrounds, and for at least 2 years.

It's not artificial. This is the tribal culture humans used to live in in prehistoric times. We are evolved to live like that.

Modern society is what is artificial.

Basically making friends is about proximity. If you want to make friends you need to live in an a tribal type community and environment.