Brazil's sugar cane-based industry is more efficient than the U.S. corn-based industry. Sugar cane ethanol has an energy balance seven times greater than ethanol produced from corn.[3] Brazilian distillers are able to produce ethanol for 22 cents per liter, compared with the 30 cents per liter for corn-based ethanol.[112] U.S. corn-derived ethanol costs 30% more because the corn starch must first be converted to sugar before being distilled into alcohol.[75] Despite this cost differential in production, the U.S. does not import more Brazilian ethanol because of U.S. trade barriers corresponding to a tariff of 54-cent per gallon, first imposed in 1980, but kept to offset the 45-cent per gallon blender's federal tax credit that is applied to ethanol no matter its country of origin
I think the reason we don't use sugar cane is that we already have the infrastructure to process corn and nobody wants to be the guinea pig and reinvest in a different method. There is also a way to turn anything that has cellulose in it into ethanol. Corn is just easy right now...