Why are US americans against helping each other?

There is no simple answer to your question. Generally speaking, the US ethic is largely built on a foundation of rogue settlers who were encouraged to take what they wanted by force and duplicity. Whether it was the attempted (and ongoing) ethnic cleansing of the tribes, or total destruction of the environment, or massacring fauna to extinction, or the brutal subjugation of African people, early americans operated at a level of entitlement, ignorance, and the absolute belief in a zero-sum competition.

This mindset has been useful to the people in power, and it has been frequently stoked to manipulate a large minority of the population into a fearful and angry existence, effectively preventing a cultural shift that embraces social enlightenment. Even the US education system is designed to perpetuate the propaganda while preventing critical thinking skills and empathy.

Interestingly, even the most virulent USers, on an individual basis, exhibit selective social welfare tendencies, while still maintaining their cultural bigotries. To be fair, most US americans are in favor of social welfare. The rich in the US, who are in control, will always fight reform, because it isn’t profitable to them.