In my early 20's, I was more open to hanging around people I know I didn't like, or wasn't compatible with, because I didn't want to be alone or without friends, craved attention, and saw every social encounter as a stepping stone and potentially valuable.
Now, I know better. When you get older you realize you don't need to surround yourself with people whom you don't like, no longer crave as much attention, and already stepped along many of life's stones. You also put on less of a pretense to others and care less about being liked. It's more important to be authentic and true, even if that means having less friends, than a phony with a lot of fake friends. All this has the result of making it more difficult to randomly find real friends.
It's common I'll meet many new people but the ones who I stay in contact with are few and far between, and that's okay. People come into your life and go out of it, it's just the way things work. I'm thankful for everyone I've had in my life and know that there are many more great people who I have yet to meet.