There's no way to sell a good, cheap car without also cannibalizing your high margin sales and the dealers wouldn't want to sell it anyway. The vast majority of vehicle cost goes to:
1) amortizing the assembly line and upfront platform design costs
2) the raw materials of the basic car components, e.g. power train, chassis, and body
3) getting the car into consumer hands (distribution fees, taxes, advertising, dealership margin, etc).
Everything else like labor and upgraded trims works out to a relatively small percentage of the overall price, often under 20%.
Since you can't make enough impact by cutting amenities, you have to cut one of the listed things. You mostly can't build things more efficiently than major manufacturers do (though Tesla is quite good here), so that's out. You can't shave 50% off the basic materials costs because you run into basic FMVSS issues. Kia's strategy is to get as close to this line as they can though. That means you need to cut from the third category. No company wants don't want to cut their own margin, so that's out. Manufacturers can't work around the dealers by law, so they need to keep some dealer margin. Manufacturers can't stop advertising because the advertising department has significant political power and can get anyone proposing that fired. Manufacturers can't avoid taxes for consumers either.
The only real paths to cheaper cars involve opening the market to competitors that aren't limited like this, for instance foreign companies that don't need dealers and are okay accepting lower margins and not advertising.