They have that incentive today. Since the government makes 18.4 cents per gallon independent of the price, the lower the pump price, the more gasoline used, the more the government makes.
American oil companies actually own very little of the oil they refine and distribute. Most is purchased wholesale from frackers or overseas.
They have become little more than government tax collectors. The excise taxes and gas taxes swamp their profit margins by almost an order of magnitude.
Same way with tobacco companies.