When you look at the best teams, they hang out a lot. They are best friends, they go everywhere together. You could say that improv caused this but there has to be a legitimate effort on the other end.
This has literally been one of the harder parts of my improv life. Sure, I have lots of friends and fellow improvisers but when I think about it, I rarely just hang out. I've come to realize that is a major issue I have to deal with.
The thing is, someone has to start the ball rolling. Organizing is hard, let's face it, but it HAS to happen. As you get better and better at improv, you get placed on teams with people whom you only know from watching. That can be hard. Rehearsals are great but that is work. You're trying to acheive something. Sure, it can be fun, but it's that extra effort that really counts.
I think I just found my New Years resolution. To take every team I'm on, and start hanging out with them. Make friends, figure out who these people are. I soon found out that those few teams I started out with, Decent Proposal, Adorable, Maybe Monogamous. I may never have those folks in a room together again. It's rough. I look back and they were such awesome people that I maybe never got to know entirely. I'm gonna try and stop the pattern. Stop the pattern and get moving.
My point is, be the one who cares enough about the team to do these things. Be the one who cares enough to make it a point to get together. Don't feel jilted if people can't but those that do will feel closer together. Get it done.