I think it’s two things: 1. What you said, politicians have little incentive to give up power on gerrymandering. 2. The American political system is designed t

I think it’s two things: 1. What you said, politicians have little incentive to give up power on gerrymandering. 2. The American political system is designed to be adversarial, and adding an “independent” agency with that much power ~feels~ like it invites distrust and corruption.