I’ve heard that before, and always wondered: how dealership owners are able to buy so much power in state capitals?

Outside of large cities, car dealership owners are usually some of the people with the most money. See also: beverage distributers

https://patrickwyman.substack.com/p/american-gentry

The same way that your local real estate development firms own your town's politics.

They care more about government then literally anyone else in the area, and nobody else has as strong a financial incentive to politically push back on what they want.

The GM streetcar conspiracy basically gave dealerships to already politically connected individuals in return for killing off streetcars - the payoff being that the busses that replaced (poorly, hence encouraging private car ownership) would be bought via the dealerships. Car dealership owners are often car dealership owners because of adjacency to power, not the reverse.

that explains all the sleazy sales practices coming from stealerships.

regulatory capture + dishonest sleazy sales practices = happy middleman, but suffering consumer and car manufacturer

A century of practice.