While I agree, that's not a genre that's mass market enough for their tastes I'd wager. But really they need to make something with Starcraft already, it's their setting with the most wasted potential if you ask me. Even an FPS could be really good, but since they canned Ghost I'm afraid they don't really trust in the IP. SC2 was likely its last iteration for quite some time, sadly.
Whatever the case, Blizzard really needs to announce new games. If Blizzconline is just the next WoW and Hearthstone expansions plus updates on D4, OW2 and Immortal I'll be quite disappointed. They've been pretty stagnant since 2016.