The workplace is one of the last places where you're forced to interact face-to-face with a diverse range of people multiple times, on a regular basis. If you're young, and from out of town, you get a lot from that.

Certainly, there are different clubs and groups out there, but the people they attract are fairly homogenous, and monofocused on their topic of interest. There are coffee-houses and bars, but you'd be lucky to interact with anyone there repeatedly in such a way as to form any durable social bond.

The only other quick option for gaining automatic access to a well-rounded social environment that I can think of is a church, but educated young people tend to enter the workforce with a contempt of organized religion that ranges from passive to visceral.