Ah, I'm one of the outliers, I have more friends now and a richer, healthier social life than I've ever had before. I'm 45, I do have a 7yo kid and wife, two dogs, a full time job, just like everyone else on here for whom these are reasons for not having friends. I have too many friends, actually, but that's a good problem to have. I make a point not to make friends with coworkers and feel bad for some of the people I know who only have work friends. It reminds me of Colin Robinson "I'm gonna go hang out with my real friends, my work friends."

Having kids really changes the game in a lot of ways. For me to consider doing something now, its not just that I'm interested or if I have the money, I also have to make sure childcare is lined up - either my partner or a family member. It makes you very judicial in what you choose to do as you have a finite amount of childcare to spend (unless you are really lucky and have a family that is always available to watch your kids).

I don't really see movies in theaters anymore because I'd rather use the childcare to go out to dinner with my wife or take in a baseball game, for example.

How much time is required to spend with someone to become friends with them?

If you assume 20 hours, that's 5-10 hangout sessions with someone. During a working life, that might take over a year. University life offers large windows of disposable time to forge those friendships. In work life, we don't have as much disposable time to spend building friendships.

Some of this has to also do w/ the environment. If you have a solid weekend pickup game of any kind and a park/rink/court closes it is pretty much the end of that group, as much as you might try to find another spot it is never the same.

Maintaining relationships with other humans is a giant PITA. It's just not worth it.

Having friends is a bit like a love relationship : you have to work at it and sometimes you get hurt. Things that are worth the effort mostly take effort.

I don't have any friends because I stopped drinking.

a lot of people see friendships as a source of free labor.