The way I see it: in general, people seem to form groups and care more about people in those groups than about those outside. What groups people form in their mind seems to be a pretty individual thing, depedent on the way one sees themselves in the world, but there are always groups and they always seem to be ordered.

That doesn't mean people don't give a shit about anything outside their closest clique! It only means that groups have different relative importance to an individual; for instance, when your family member is sick, you might temporarily stop attending the soup kitchen and spend that time helping the sick kin.

My point is that such "ordering of care" is part of our firmware, and because capitalism is compatible with that, it's easy to implement by humans - in the same way the basic concept of private property seems to be also a part of our firmware, and more extreme parts of communism being incompatible with that meant people started to work against the system.

Basically, if your system aligns well with natural tendencies of humans, it's easier to make it work. Corollary to that is that you should design your systems to work with natural tendencies of humans, instead of trying to change those tendencies directly.