But you know who probably did? Activision.
Diablo Immortal, or How to Read a Room

Blizzard, Oh blizzard. I don’t even play Diablo and I am disappointed in them. From my knowledge, Diablo is a massively popular MMORPG sort of like path of exile. At this point, I think that Blizzard has fallen into to money trap so to speak, or at least sold out to Activision. By this, I mean that Blizzard or at least the people responsible for Diablo value cash over making what the consumers want. This to me, is sort of similar to a game developed making basically the same game or similar game each ear with minimal changes. For Example the Fifa or Call of Duty franchise. Right now Blizzard has forgotten how to make a great product and cares only for the cash and microtransactions. However, Blizzard does have complete control over their product. If they want to make mobile games like Skyrim Blades and now Diablo: Immortal they can totally do it. It just doesn’t mean that people play those mobile games over a PC game. It also could be completely possible that Blizzard released a Mobile Diablo while they work on a bigger better PC Diablo.