I don't get this selfish lack of solidarity towards your fellow humans.

It's because the US is far too big. People in one part of it have a very different culture to people in a different part of it, as a result they find it hard to empathize with them because their lives are so completely different. The problem is that they are all one country and operate under one government.

The individual state governments help a little bit (except when they're trying to write laws to one-up each other), but basically the US government is trying to implement laws that will apply across wildly different cultural ideologies.

From the highly religious almost zealot south (Texas, Florida), to the mostly secular north east (Washington), to the liberal west (California), to the farming belt in the Central regions.