Blizzard ended last Friday's BlizzCon keynote on an announcement that earned immediate derision from the majority of the developer's fans. Diablo Immortal, an action RPG on mobile, was the clincher. As the reaction over the weekend has certainly confirmed, many many many people did not want a mobile Diablo to serve as BlizzCon's major reveal.
There was nearly a bigger announcement that would've taken some of the heat off of Diablo Immortal. According to Kotaku, Blizzard was intent to end the BlizzCon keynote with a quick video from co-founder Allen Adham where he would tell the viewers that Diablo 4 is in development but that it wasn't yet ready to be shown off.
However, Blizzard backed away from those plans in recent weeks. Kotaku's sources say that the Diablo team wasn't comfortable committing to a proper reveal, even one as soft as a simple confirmation that the game is being made. That's because Diablo 4 has evidently undergone major direction changes over the past few years. Those closest and most influential to the project seemingly aren't confident that its design is cemented.
Blizzard knew what kind of reaction was coming. Otherwise, what reason would there be for the public request in October that fans temper their expectations? But it was backed into a corner at that point. Without the Diablo 4 bombshell, Diablo Immortal is all the Diablo it had left. A Diablo mobile game was never going to satisfy the series' most hardcore players. That doesn't mean it won't be wildly successful, though.
Lost in the cacophony of disappointment is the fact that Blizzard has implicitly all but confirmed Diablo 4's existence for years now. That aforesaid October request mentioned that Blizzard is working on "multiple Diabloprojects." Every so often, there's a job listing that pops up for an unannounced Diablo game. Blizzard is clearly still making more Diablo.
But, Blizzard works on Blizzard time. An announcement wouldn't mean anything was imminent. It'd still (likely) be years before Diablo 4 ever released. Waiting is an expected part of the process when it comes to Blizzard. Diablo 4 is coming but Blizzard isn't going to rush it.