Classic WoW was designed by Blizzard devs. As stated by Chris Metzen, in Classic WoW the World is the main character. It was the "World" of Warcraft.
Battle for Azeroth on the other hand was designed by the WoW playerbase. That is the MMORPG this community ended up designing. All the complaints and demands by members of forums like MMOChampion are what created Battle for Azeroth.
Now how did we get here? Why is Retail WoW no longer an MMO or an RPG? Why is the World gone? Why has Retail became a singleplayer lobby based game? Because the playerbase demanded it to be this way.
When did this shift begin? It actually began midway through Vanilla. Players began complaining about Battlegrounds. They didn't want to have to run to the instance portals in Arathi Highlands, Alterac Mountains, or Ashenvale. They wanted to queue for every battleground at once. They wanted to teleport to the instances and not have to wait. Blizzard caved in. They added Battlemasters which allowed players to teleport into instances across the world. Instead of running across the world zones, you could now teleport past them. You now had players standing in the same spot in Ironforge and Orgrimmar queueing over and over again without leaving the room. This was only the beginning.
The Burning Crusade brought flying mounts. The community thought it would be an "awesome" idea. Land mounts were too slow and clumsy. This not only shrunk the world, but also lessened player interaction in the zones. Compare your experience riding your mount through Kalimdor in Classic to using a flightmaster to fly across it. Flying literally allowed players to bypass the World. Imagine flying at 280% speed compared to running at 60% on land. There are literally members on this forum arguing that flying mounts increased player interaction and World PvP. How delusional can you be? Blizzard capitulated to players like this.
Players complained. Wrath of the King gave us crossrealm dungeon finder.
Players complained. Cataclysm gave us crossrealm raidfinder.
Players complained. WoD gave us sharded crossrealm zones.
Communities like MMO-Champion are what spawned something as lifeless as Battle for Azeroth.