They’re expanding the whole of Leavesden studios aren’t they, I think Warner wanted it to be the home of the DC universe.It's also tapped out in capacity, they max out every year (barring the covid year) so whilst it is a steady stream of income it is also a limited stream of income. I have no doubt that Universal pays more per year than the Studio Tour makes and I'm not including royalties either.
Which brings us to UGB, if it had Potter I'm very confident it would bring in more via licensing and royalties than the Studio Tour does, just on the sheer weight of it's increased attendance. But that's something the execs and JK will have to consider here.
The Studio Tour itself may not even need protecting from UGB, it's popularity is such that it could easily live among UGB without seeing a huge drop in visitors. But it's up to Warner whether they want to risk it or not and right now it seems Warner are being cautious and not wanting to risk their stable income.
*edit* I do think the Studio Tour is actually a red herring here. No, I think the crux of the issue lies in Warner Bros probably asking for a far higher licensing fee and royalty rate than what has come before and Universal are reticient to pay those exorbitant amounts when they can replace Potter with LOTR at a drastically reduced amount.
I assume they’ll also be filming the new potter show there for ten years.
I also assume they’ll be expanding the studio tour if they have any extra space once they’ve completed the expansion, whether that’s stuff from the movie series or the new tv show who knows. But tbh they’d be stupid not to.
It’s extremely profitable for Warner.