Because our political system has been taken over by entrenched authoritarian conservatives who have rigged the game such that it is very hard to remove them.

That combined with the fact that the majority of Americans are struggling these days financially, and you have a situation where people care, but they care more about putting food on their table for their family and keeping a roof over their heads, so that stays at the top of their priority list and they don't have time to be active enough to do something about this.