Why would you ‘shut up’?

Concessions are given, the radicalization stops as the standards of living improve. People are satisfied and don't pursue the deeper systemic issues. Once the radicalism has died down, efforts are made to remove those concessions. Sometimes it does not work, a lot of the times it does. The rise of neoliberalism was one of these efforts, the most succesful so far.

Passed laws just don’t evaporate into thin air after they’re done being passed, they continue to exist.

They don't evaporate, they get repealed. Tons of things do. Roe v Wade, police defunding, literal underage labour laws got repealed this year. The Paris Agreement almost worked, but thankfully protesting brought it back.

Not everything was about slavery.

I'm not talking about slavery. Every fundamental working right we have comes from fighting. The 40-hour work week and 8-hour work day, the abolition of child labour, the minimum wage, pensions, sick leave, paid overtime, the right to strike... even weekends are thanks to fighting. Look it up if you don't believe me.

You may notice some of these things have been dissapearing recently, and that's exactly what I'm talking about. They were concessions given to us so we stopped being a threat. They don't perceive us as one anymore, and so they're trying to gain more power for themselves by stripping us of the things we earned. And part of this threat reduction is precisely the insisting on working within this "democratic" system, which will never meaningfully challenge them, because it is for them, by them, and controlled by them.