Airline mileage programs existed before hotel loyalty programs. In the '80s and '90s, many hotel customers desired airline miles, and hotels gave their customers the opportunity to earn miles to attract business.

The main reason airlines do not give hotel points is economic. Most American airlines are losing money, and they want to tie their customers to their mileage program. Hotel companies have been profitable and have greater pricing power than airline companies. Thus, they have more money (and willingness) to allow their customers to earn miles in lieu (or in Hilton's case along with) hotel points.