It wasn't because in the old (and proper) lore Sargeras himself became 'corrupted' and lost hope. He stopped caring about life. The new crap lore has Sargeras still caring , which makes him a massive retard considering NOTHING stops the Void Lords from corrupting life again if it reappears.
At best, this new shitfest they call lore is incomplete for now. At worst their retcons were badly thought out and it'll just be more garbage like 'Alternate Draenor'(likely).