Because it looks like we are getting more of it!
Trump said yesterday that he would direct the EPA to allow sales of E15 during the summer, when it is currently banned due to air quality concerns.
Farm states are obviously quite happy that we will be encouraging more wasteful corn production.
Meanwhile environmentalists are upset that the decision will cause smog a decrease air quality and of course the fact that ethanol production (at least from corn) is not at all environmentally friendly. Oil refiners are upset because they wanted a broader package of ethanol reforms, but with the farmers getting what they wanted, they will no longer have incentives to compromise on things the refiners want.
Of course allowing the sale during the summer doesn’t force oil companies to sell E15, but the speculation seems to be that the shift will create the right incentives for a switch from E10 to E15 as the standard gas.