And its their own fault. Dota started off as a mode for their game. They were fully aware of its popularity, even made changes to custom map size specifically to cater to Dota and the people who played it. Yet they never made the move to turn it into a stand alone game and Valve stole that golden goose. And now when Heroes of the Storm was finally put to rest they basically gave up the MOBA dream.
Although Valve did fail with their card game while Hearthstone is still running strong so I guess they are kinda even.