RE: People Don't Care Unless It's Their Interest

I believe this question is based on perspective. Just as you mentioned, people cannot actually care about everyone and everything they come across. They are some people who show compassion regardless of the circumstances and they are some people who don't. We should just go about our businesses not putting too much hope in humans.
People will only care about you if you're a priority to them. It's not selfishness, it's just how we're wired.