Quote Originally Posted by Tiwack View Post
Because it's easier/cheaper to make entirely new zones than layer on new stuff on top of the old zones, it's much more prone to weird bugs and requires a lot more care to pull off. From the effort/reward pov of devs and beancounters it's clear why nothing is happening with the old cata zones and whenever something does it's simply put into an instanced scenario so they don't have to mess with old code and avoid the mess it'd be altogether to edit.
This. Remember the Chamber of the Heart and how buggy it was by the end of BFA having gone through like 50 layering changes?