Unfortunately sales kinda tanked between seasons. From 7,368 average to 3,397 average, and there's little reason to believe a third season would do any better. I bought both seasons, but I guess I was in the minority. Similar to but not quite as bad as the drop in Milky Holmes sales, hence the "IkaMilky" meme on 2ch regarding sequels that drop a lot.
OADs like this make a lot more sense economically than animating a whole new season when you know you can expect sub-4k sales at best, and the main advantage new animation can bring to the franchise at this point is to drive more manga sales - so you might as well bundle something with the manga directly.