Why is opposition not highlighting 20% ethanol blending of petrol?

The union petroleum ministry has made E20 fuel mandatory for petrol which means the petrol sold has to contain 20% ethanol. Now ethanol has lower efficiency compared to petrol and so this results in lower mileage for the same vehicle and also damages the engine. This is not very technical and any car user can find out. Also, Nitin Gadkari is heavily linked to sugarcane farming industry and is benefiting hugely from this. The conflict of interest is so blatant. And yet, the INDIA alliance doesn't talk about this at all. Why? This affects every state equally. And they have not reduced the fuel prices for ages! The loot has a visible and quantifiable impact.