The United States government has added tax exemptions for those that are purchasing green vehicles. Because of this, I can save money in regards to buying a new car if it fills their quota.
Another benefit would be the amount of money that I save on gas. Due to the less amount of money needed to fill up my tank, the amount of money that I save could then be used to cover the cost of the vehicle, or used for something else.
The last reason would be the variety that there is with fuel efficient vehicles. There are a lot of options to choose from whether if someone has a family, or it's just for two people. With the large variety of options, people are allowed to have more choice in regards to what they could buy.