Sometimes you get complacent when you become the big dog. No longer hungry. No longer innovating. Bitmain is raking in so much they just stopped innovating. With things the way they are, they might ease out of their slumber and try to cobble something together. Who knows.
Can't "innovate" when your state-of-the-art product is already on the current "industry best" production node - which is WHY they have not released anything better than the S9 and probably won't for at least another year, no new node with significant performance upgrade has any capasity AVAILABLE to them, and it takes many months to a year to design a new chip on state-of-the-art nodes.