Both major parties in the US benefit from maintaining the status quo. Neither one wants to do anything that takes power away from Congress and puts it back in the hands of the people.

Whichever party is in power during any given cycle is the one that benefits from gerrymandering, omnibus bills, fillibusters, etc. So why would they change something that's useful for them?

Then when the pendulum swings to the other side of the aisle, the situation still holds true. Party A and Party B will fight each other to the death, but neither one wants a Party C to rise to prominence.