The benefit is an advantage in a competitive market. Ethanol competes with gasoline which has the taxes. They are given an economic advantage that market that other conventional and unconventional processes do not have.
Apparently, you either don't understand the point, or you're just being purposefully obstinate.
In any case, ethanol receives no subsidy. Rather, it receives preferential tax treatment, which could be said to have an effect similar to that of a subsidy.