I don't think having UNESCO status means that you can do
nothing - it's that you have to be careful with what you do if you care about keeping this status. If you look at the main photo on The Guardian's article on this subject (
https://www.theguardian.com/uk-news/2021/jul/21/unesco-strip...) you'll see that there's a bunch of generic glass-and-steel buildings that have sprung up around that area. The BBC article went with pictures that
do not show this for some reason, and it's easy to come away from that article thinking that Liverpool has been punished for just tidying the place up a little bit, when they've done some pretty substantial development that really changes the character of the area.
As someone who is neither an architect nor personally involved in UNESCO I've no idea what they would have considered acceptable or compatible with World Heritage status, but I am sure that there is some way that land could have been developed in a way that wouldn't have drawn their ire (like not planning a 55000 seat stadium, for example). Whether Liverpool would have considered such a development worth it or not, I don't know.