I hesitate to throw out this quote because it may come across as a "hot take" but I think that John Steinbeck said it best:
"Socialism never took root in America because the poor see themselves not as an exploited proletariat but as temporarily embarrassed millionaires."
Another quote I've heard is that "extremists become more extreme, not less, as problems come closer to solutions."
"Socialism" and "extremists" don't really apply but the sentiments do. Unions sprang up in the United States as a counterweight to outright and absolute worker abuse. Things we--those resident in the U.S.--now take as "absolute," like child labor laws and the 40-hour workweek, were earned as a result of those early struggles.
We've had it really good here for really long, comparatively, so I think that a lot of people see these kinds of abuses as "won't happen to me"-ism so they're not interested in sacrificing even a little to ensure that the abuses happen to virtually[0] no one.
Going back to unions, a lot of people I know--in the IT industry, obviously--flatly refuse to recognize that a union could be a good thing because jobs, salaries, and opportunities are all plentiful. We're not "abused" because employers know that we can just hop jobs and recover. (Never mind things like the gaming industry or the "crunch" period or, say, Uber.) Because of the illusion of choice, unions aren't valued. (I say "illusion" because witness what happened in the doldrums of the early 2000s. When every employer, or even a bunch of large employers, pull back at the same time, there is no choice.)
For others, things like unions or some form of collective action or even just "group health care run by the government" are seen as impinging on the basic rights to shoot--metaphor intentionally chosen--our own feet off however we like, consequences be damned because other countries are just wrong and the United States is a Special Snowflake.
Or something like that but maybe with a little less bite.
0 - I say virtually because people will always find a way to take advantage of others but there's a lot to be said for pushing to prevent that as much as possible. America doesn't seem to do that very much.