Because people still have things to lose and the law is selectively enforced.
A nigger stabs a White man and he is let go the next day but if that White man lays a finger on a nigger or a jew he is going away for decades and the cops will be OVERJOYED to beat him within an inch of his life for even thinking of fighting back.
The cost or resistance is very high in the US, if you want to fight back against jews you have to be willing to kill cops and judges who serve and protect them, that's too high a bar for most people.
Kikes don't just import a foreign army they make sure Whites are demoralized and deracinated so they can't fight back. They attack the mind before they attack the body.