It's all just guesswork, but projects are greenlit by those high up in the companies, so while some developers most definitely love making games on mobile when you work for big publishers they are the ones who decide which games are going to be made. As far as Blizzard's whole deal with the new Diablo is concerned, I just think it was a bit tone-deaf of them to say something like that at Blizzcon. Considering Blizzard's history, I would guess that a majority of the people in attendance were PC gamers at least to some extent. I'm not sure what kind of reception they were expecting when they tell that audience that a Diablo game isn't going to be on PC..
One could argue that making the announcement at BlizzCon, which in turn made all of this noise, was a very smart move. Would we be talking about it right now otherwise?