I think people underestimate just how much money the WB Tour generates, they've been consistently raking in 100 million (£) plus in profits annually, with their profit margin reportedly being 55%, It's insane, and 2023 was a record year for them too, despite no kids being old enough to have seen a movie on the big-screen, so it's all older folks with disposal income who want to be immersed in that Harry Potter universe.
There is zero chance an amusement park with it's running costs could come close to that profit margin and return on investment, so the WB Studio Tour and HP stakeholders have nothing to gain from any sort of deal or collaboration, and have every reason to play hardball and stop USGB ever getting anything even remotely Harry Potter related.