Why do people make their problems other people's problems?

It feels like everyone is so comfortable letting their negative emotions affect other people and I don't get it. It's rude af and, frankly, selfish. Obviously there are times when things are more serious and I can understand why someone wouldn't care enough to hide those emotions but still. I seriously don't get why people want to spread misery. All that "hurt people hurt people" ish is such a cop out.

When it comes to this stuff, I don't really have the patience for people I'm not close with. I'll either confront them or just dip but with family, it's different. My dad and I are similar in that we don't really complain, we fix our own problems and have a "make lemonade" kind of mentality but my mother and siblings have the "if i'm upset, everyone's gonna know about it and no one else can be happy" kind of one. I loathe this trait in a person. I really do. It feels like the air is way thicker and I'm just walking on egg shells, waiting for the other shoe to drop. Like why would you want someone to feel like that? Why is it anyone elses problem that you're pissed or upset with something? Deal with it in your own way. Don't let it affect people that have nothing to do with it. Purposefully making someone feel like sh*t just because you are is c*nty.

I don't even know how my family would react if I were to be a mopey b*tch around them. I can honestly say that my mood or emotions have never been the source of an entire mood shifting for the worse. Even as a kid. I take pride in making the people around me feel happier or at least not worse than how I found them. I don't know why others don't strive to be like that. Obviously, not to the point that it takes a toll on you or you're being fake but yeah. I just leave the situation when that's the case.

The older I get and the more people I meet the more I notice how common it is. It's depressing as hell.