I think you find your question offensive because it is poorly framed. I think a much better question is “what is wrong with our mental health infrastructure in America? Why is it so awful that we feel we must ask what is wrong with the mentally ill?”

To your point at not seeing mentally ill people in poor societies: I bet if you really follow this logic, you can figure out where these people are in those societies. Jail, other captive institutions, too ill to be in public, violence, institutional or personal, and death are all valid