Capitalism is about taking everything you can, to act as a balance against everyone else doing the same, because the fundamental assumption is that greed is the natural state for people and we shouldn't try to fight it. Under capitalism, competition doesn't just apply to businesses in markets, it extends to everything: people must compete with those around them for resources (be it jobs, or food, or retirement investments), making human connection a primarily adversarial relationship.

Now nothing says that you must apply capitalist principals to every aspect of your life if you live in a capitalist society, but it slowly becomes the norm. Eventually, the reason people take care of eachother because is indirectly benefits themselves, rather than because its a good thing to do... And when that's your justification, it's easy to stop doing it.

It's all about establishing norms about how people should treat eachother. Under capitalism the norm is adviseraial by design, but under communist it was supposed to be cooperative. It didn't even up working that way, but that is the ideal we should strive towards.

Edit: fix typos