The dealership owners are self-interested so they lobby to make sure the current system stay intact, and are reliable campaign donors who make sure they cozy up to politicians.

The politicians are motivated by the campaign donations they receive and know that if they cross the dealerships they’ll lose those donations and probably also see those lobbying organizations contribute to candidates running against them.

And the fact that an individual politician isn’t working to dismantle this crummy system probably won’t ever cost them many votes, or gain them many if they do try to reform it, so what’s the motivation to upset those donors? I mean we both moan about this but it’s not like you’d vote for Elizabeth Warren in the next go if she made this part of her platform (ditto me and, say, Ted Cruz).

So it’s one of those things where a broken system keeps a crummy outcome entrenched.