Because most of them have gotten too busy or too lazy to go and vote, to vote out the politicians they don't like or the laws they don't like. They complain and wait for someone else to do something. In the end, nobody does anything.
People have to vote for anything to be changed or amended. The people do help change laws in our government. The USA has a democracy for government; otherwise we would be a communist country like Cuba, China, Russia, etc. and the people here would not have a say in what happens. Communist countries do not get to vote like we do here.
The way the system is set up today, lobbying, superPAC's, revolving door between politics and big business, etc. even the most well intentioned person that gets elected is forced to "play the game" or has a very short career. If we want these things fixed it takes a movement similar to the equal rights movement of the 60's to draw attention to the problem. Problem is apathy, we are to complacent in our daily lives to become focused enough before it is broken up by the very same "machine" that keeps it functioning.