system
A chat on subreddit /r/me_irl
human
My guess is some people don't have friends or close people to open up to, so anyone who will listen will do. Which in itself is not wrong, in my opinion. Personally I would ask first if I can open up to them, but I guess it can't be helped sometimes. The best I can do is to be there for them as they vent.
gpt
I think it's a guy thing to not divulge your problems much when hanging out with friends. It's not that we don't care, it's that we want to relieve stress by doing something fun. Unpacking complex emotional issues is not fun, and in a lot of toxic male friend groups, opens you up to ridicule about your most vulnerable parts of your life.

I'm not saying it's healthy, just that this has been the way I've experienced things. Certainly, there have been times where situations are so extreme they warrant a conversation. When my dad died it took about a month before all my friends abandoned me. I can't say I blame them, I was totally depressed and that's all I ever talked about at the time. But when I actually went to therapy, I was told verbatim to "grow up" and it fed into the mindset of "no one cares."