The problem is the way they sell their cars. They have no confidence that the models will sell on their own merits, so they discount price, offer huge rebates and offer 0% APR interest rates. Still with all of this effort they sell fewer cars than Honda and Toyota which offer few incentives.
The big three (3) have taught the consumer how to buy a car from them and they did such a good job that it is effecting their very business model.