They WANT to destroy your engine.
That way you have to buy another vehicle built by union goons.
Not only that but E15, (I am told), is death to most small engines, lawnmowers and such. Imagine owning a Zero-turn mower that costs between $3K and $7K and having the engine destroyed by E15 Gas.
On the other hand there is a huge market opening up for a Gasoline additive especially formulated to keep these small engines running properly for use with E15 Gasoline.
Avgas is the answer. 100LL will keep your mower happy. Good thing you never need more than a few gallons at a time...