I don't care about other people's lives and I don't want to know about their problems
Why don't you want to know about other people's problems?
Because it isn't important if I don't know them. If I don't know them then I don't have to care.
Even if you don't know someone personally, you can still empathize or sympathize with the issues other people are going through. You don't have to be involved in everyone's problems, but it can make you a kinder person to know the struggles that other people have to deal with.
I try to be a better person and care about everyone but I just can't for some reason. But you are right, everyone's problems aren't mine to care about all the time.
Sometimes just being there for someone can be a huge help, you don't have to have a solution for every problem. But, if people are taking advantage of you or oversharing, you should advocate for yourself and protect your own mental health.