Have been following this via several forums for a while now, I think the most likely explanations are legal and jurisdictional rather than technical.
Technically I'm sure it would work just fine, the app couldn't care less where in the world you happen to be when you tap the screen to make your bookings.
However Disney needs to follow the correct local legal processes for
wherever the user is currently based when it stores their data, and that's for nearly 200 different national legal frameworks. In the EU and UK, that would mean following the EU's over-bureaucratic GDPR for example, and most other countries have their own equivalents defining how their citizens' data can be processed and stored. Unless Disney is 100% sure it is working correctly within ALL of those legal frameworks, they aren't willing to risk the consequences of breaking some local data protection law accidentally.
A current example would be booking events and tours. None of those can be done on the Disney UK website by default, the option simply isn't shown on our ".co.uk" version of the page - which you are forced to visit by Disney's regional redirection code, even if you try to use the ".com" address. However if you first use a VPN to pretend you are in the USA, the booking options become visible and bookable. I fully expect LLMP will work the same way (possibly using GPS on phones rather than that IP-address based geolocation) but we shall have to wait and see.
Disney.co.uk web page view for Horse-drawn carriages for example (no 'Check Availability' option is shown):
View attachment 877005
But with a VPN set to indicate a Miami based IP-address, bingo I can now see availability and make a booking:
View attachment 877006
Andre