Honestly, I am not sure if Diablo 4 was on the cards at all for them. Diablo 3 has not been supported for ages, and cash based auction house was not the best long term idea. Clearly activision is chasing the moolah, so in the absence of being able to easily monetise it themselves, looks like they outsourced it to someone that could, would, and subsequently did. Not surprised fans are pissed tbh. Ripping apart one of the great pc gaming legacies with surprisingly few titles needed to get there. If they actually release Diablo 4, I hope it is better than just an afterthought