US citizens are literally wage slaves, who can be fired for no reason and whose healthcare is tied to employment.
The country is immense with vast distances between major cities, so in order to protest in a meaningful way (ie, not being a scattered handful of picketers in towns hundreds of miles apart that would get no press traction), people need to take weeks off work which would get them fired and take away all their healthcare and retirement options, and drive the equivalent of several EU countries, then hope they have a home and job to return to after. And over a century of unchecked capitalism has locked people into a cycle of perpetual debt such that many are only a paycheque or two away from losing everything.
It’s not an excuse, but a compelling reason that is exploited by bad actors in the government. They know with no safety net and literally everything working against common people, it’s very difficult for protests to gain purchase.