probably fear of sunk cost on the deal, giving up a sure deal with 80% of the profit you expected instead of 100% is still making a profit.

This might work for used cars, but probably won't for new cars. Dealers frequently lose money on the sale price of new vehicles, but make up for it on finance/insurance and profit from selling any trade-ins.

Certified pre-owned vehicles will often have a better warranty than a new car anyway and you don’t lose half the value driving it off the lot. Win-win.