Because I'm not a violent person? Believe it or not, the average American doesn't want to murder and create death on the scale necessary for that kind of change, which would be followed by years of uncertainty and gambling that the new set are better.

Substantial change has been created, repeatedly. Suffrage, 14th amendment, the later implementing of the 14th in the 60s, the judges appointed were also appointed by people who were voted in who voted to expand gay rights and desegregate schools. Further more you have a large amount of smaller, but none the less immensely important changes like health codes and building standards that made the world considerably safer and lessened the ability of workers to be abused in a health way. Despite the recent backslides, we have immensely progressed as a net result. You have even lately expansion of socialist projects like public transit, and city land trusts which are a form of semi socialized public housing.