Because America is a Democracy. Non violent protests changed people's minds and those people ultimately decide the laws. Won't work in China. China is totalitarian. The government gets what it wants regardless of public opinion. And it will squash any opinion it doesn't like before it spreads.

That worked because the federal government had guns and Civil Rights had widespread support in much of the rest of the country.

History is probably full of deaths of nonviolent (and violent) resisters.