The way they announced it as their biggest title of the show was their downfall. Everything could go well if they had a PC Diablo game announcement right after DI.
I know how big the mobile market is, take for example: League of Legends, the most popular MOBA worldwide, made a revenue of 2.1 billion dollars in 2017; but there is a chinese knockoff of LoL for mobile devices called Arena of Valor, which made over 3 billion dollars during the same year.