Much of this falls down to the problem if instancing. And why many developers realized that while it might be interesting in theory to have everything happen in the overworld, it would be a nightmare to balance the player economy around it.
Molten Core for instance could not really function as an overworld area, you could just pull all the bosses to somewhere with NPCs and have them kill the boss for easy loot, or maybe the boss was just killed by someone before you got the raid group together and you have to wait for it to respawn.
Similarly with PvP i imagine the devs wanted to have more overworld PvP stuff, but they realized that doing so would be detrimental to the experience. We saw this with Ashran, where battles ended up as endless tugs of war where the winer was determined by who had the biggest premade. This was eventually changed to being grouped up instantly, but then the battles simply became an endless back and forth where teh sides essentially took turns winning.
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And what makes you think that?
They have raids, dungeons, levelling stuff, a story planned, a new way to structure the endgame overworld content.
Nothing so far is implying Blizzard has no idea what to do, mostly it just seems like they are trying ot prevent themselves from overcomplicating the core formula of the game.