From experience, the difference is entirely in the way our societies are setup, and therefore how we treat each other.

In NZ/Oz/Canada, we have healthcare for all, affordable tertiary education, and we all pay higher taxes to help strangers. Looking out for each other is built into the makeup of our countries, systems and society.

In the US, it is literally "Me vs. You", "Everyman for himself", "Pay your own way", etc. It is simply not in the makeup of their society to help others. While of course there are extremely kind and generous people who do, it's not the way the systems are setup, so it's not the default way people think about things.

Also because tens of millions of people are within a millimetre of bankruptcy/starvation/living on the street, they literally have no head space or ability to do anything other than meet their own basic needs.

Here in Canada tens of millions of people have been getting $2k every month since March. Same in Australia.

In the US they got $1,200. ONCE. That changes a lot.