Cultural history. A lot of it is propaganda, dating back to the 1920s, and even earlier, to the 1890s, the age of the Robber Baron. There was an unbelievable amount of poverty, people working 60+ hours a week while living in squalor. Massive labor strife resulted, lots of deaths.
It was the dawn of both socialism, and labor unions, which were absolute anathema to the business tycoons. Socialism was perceived as a threat to the wealth and power of the tycoons and they fought back with everything they had, and one of their biggest weapons was propaganda.
One theory about the cause of the Great Depression is that it was caused by an over-concentration of money. Too much money in the hands of too few people, not enough circulating in the economy.
To deal with that, FDR went full socialist, creating the modern US welfare state. The capitalists hated this--but it was this, or face a possible second civil war. It was also FDR's attempt to head off a government takeover by socialist parties.
Then World War II happened, and the capitalists lost much of their control over their businesses, as the US went to a war economy, with wage and price controls, rationing, and many other new controls constraining what the tycoons could do. As a result, american workers experienced better pay and better working conditions than ever existed before in US history. All essential to the war effort. This lead directly to the postwar boom.
In the 1950s, though, the capitalists fought back. The era of the Red Scare. Huge amount of propaganda, like you wouldn't believe, and it was everywhere. I saw a lot of it reading my uncle's magazines from the 1950's when I was a kid. Magazines like "Popular Science", "Popular Electronics", "Popular Mechanics" otherwise not associated with politics, were full of anti-communism articles, and "beware!"
The propaganda was very successful, and anything even vaguely socialistic became directly associated in the public mind with evil totalitarian communist police states. "Beware! They're covert! They're trying to destroy our American way of life! Don't let them win!".
As a result, few Americans know much about socialism at all, especially on the right. To them "socialist" is a boogeyman, leading straight to North Korea and the USSR gulags. It's become associated with police state communism.
Few conservative americans even know much about socialism at all. "socialism" evokes North Korea, not Sweden and Norway and Denmark. And they don't tend to think of many of our institutions as "socialist"--like the parks, public libaries, police, schools, roads.
It's the primary reason the US has had such a difficult time getting universal health care. The propagandists have been extremely successful at getting it associated with police state oppression and deprivation in the public mind. To the point where a photo of a protestor holding a sign saying "Keep government hands off my medicare!" went viral, because it's so clueless and ironic.
Americans went conservative in the 80s, because of staglation and the energy crisis in the 70s, and Ronald Reagan promised "Morning in America" and told us "government doesn't solve the problem. Government is the problem", promising to get government off our backs, and that the prosperity will trickle down--none of which happened. Americans are starting to become disillusioned, with conservative ideology. Maybe.
So now there's Bernie....educating many Americans, "I'm a social democrat, not a communist" "My model is Sweden, not North Korea".