Why is the social security level in the United States low?

The welfare of the United States is not good in developed countries, and it is also the only country in developed countries that does not have universal health insurance, which is related to American culture. Americans believe in the American dream. The so-called American dream is that a poor man eventually becomes a rich man through his own efforts. What is emphasized here is the spirit of individual struggle, not government relief. Watching Hollywood blockbusters, the protagonist used to be miserable and often slept on the street, but he worked hard and eventually became a rich man. Moreover, conservatives in the United States often criticize the poor who receive government relief, such as the party, the tea party and other Rightists, and often criticize the government for helping the poor. They think these people are parasites. They are poor because they don't work hard.