Why does Stormhaven lag so much?

[Aku]

I have noticed for months now that Stormhaven lags like no other zone. You travel to the Wayrest wayshrine and get stuck on the loading screen. You finally transition and when you call your mount it takes several seconds to appear. You go outside the gate to the Undaunted camp and none of the NPCs or fixed objects are loaded, and you have to wait twenty seconds for things to spawn. You log in where your character is in Wayrest and get stuck on the load screen. You exit a delve in Stormhaven and get stuck in a load screen. Why doesn't ZOS work on fixing these things instead of just adding new content?