you're presenting this a little bit disingenuously. expectations were high that diablo 4 would be announced in 2018, and instead there was the announcement of a partnership to develop a mobile version of diablo. folks were upset and the presenter reacted poorly.

the following year diablo 4 was announced and much was forgiven. the mobile game is still not out (in closed beta rn) and early reports are good.

you can fault blizzard for thinking its core fans at blizzcon would be excited about a mobile game, but if you are a game developer with a popular IP you're making a huge mistake not developing for mobile, as it will be the majority of the global gaming market for the foreseeable future.