While U.S. refineries supply much of the demand of U.S. consumers, imports of finished fuels are still relied on. Between two and three million barrels of finished fuels are imported to the U.S. each day while nine million barrels of oil are imported daily.

So- the answer- is the fact that no new refineries causing prices to rise?

No. While there have been no new refineries, expansions have increased output since the 70's and 80's.