If we were religious, we would say God made them this way.
But since we are rational people we accept that not everyone is born like little Buddhas, without mental health issues. There are many natural disorders that occur naturally in peoples brains, but there are also many people who struggle in life because they are not taught good coping skills. Others live is high stress environments and struggle to cope with helplessness. There is also a lot of negative influences, some of which people invite into their lives, like racist views of those around them. More mental health care access would help people learn and cope better.
The USA has a subtle philosophy of everyone for themselves, and it just doesn't work.