Because the power imbalance got too great.

my conspiracy theory is dopamine addiction. The price of everything goes up way faster than the things that entertain us. I think this is intentional, they stopped giving bread but keep up the circus.

Machine guns, armored vehichles, and chemical weapons happened.

At least in the US, the bourgeoisie was successful in breaking working class consciousness and solidarity. Technically speaking, we could always protest and bring up arms against them, but without these things, not enough people recognize the truth about their oppression and work together against it. Though from what I've seen, things are starting to change.

Divide and conquer aka culture war. Too many people were convinced that brown people, queer people and women having abortions are what's threatening their wellbeing instead of capitalists exploiting everyone.