US Oil received 44% of US Energy Incentives, 1950-2010

Why is it that the Oil industry, the world's most profitable energy sector, has recv'd 44% of all US energy subsidies since 1950? I don't get it. 

 A new report commissioned by the Nuclear Energy Institute, 60 Years of Energy Incentives: Analysis of Federal Expenditures for Energy Development, shows the following lead chart.

(Click to enlarge)