peasant revolts were extremely effective throughout much of human history
They still are.
The only separation between now and then is perceived isolation from power.
If even a fraction of the working class people rose up and wanted to, I dunno, kill trump (theoretically) in the US, right now, there is zero goddamn way the US gov could stop them. Theyd be outnumbered 10,000 to 1, easily.
The only thing stopping everyone from doing it is the notion that they cant do it.
Lord knows we've seen in other countries plenty of younger generations take down their governments with ease, so the capability is 100% still present.
My honest opinion is its just a case of Bystander Effect. As your population density goes up, the Bystander Effect spreads out beyond just immediate vicinity and to the entire city/state/country.
No individual state wants to be the one to stand up and fight directly, so everyone just stands by and watches.
No individual group of people wants to be "that" group in the US, so everyone just stands by.