It's almost as wild as when during the pandemic "lockdown", planes had to take off, burn tonnes of fuel and land empty some minutes later at the same airport, because there's some fucking law about landing spots and how they'd be lost if that bullshit wasn't done.
Before the COVID restrictions, airlines were required to use their allotted spots at least 80% of the time.[6] During the pandemic, the European Commission temporarily suspended Europe's airport slot rule for a short period.[citation needed] Due to travel restrictions, many flights were cancelled or had limited capacity, which made it difficult for airlines to fulfill all the requirements for possessing an airport slot. The suspension of the slot rule was reinstated in October 2021. After the slot rule was reinstated, the rule only required European airlines to use 75% of their flight slots for the winter season.
https://en.wikipedia.org/wiki/Ghost_flight_%28commercial_avi...
Also if you do revert account to UK you will get a warning that you either need to disable ADP or lose access to iCloud features.
Unlike Android there are way more hassle in installing iOS apps under different accounts with different regions. On Android I just have 5 diffetent accounts with different billing countries and it just work.
Also AFAIK iCloud family features dont work cross-region.
From what I remember it uses a combination of things like your current GPS location, your SIM cards reported country and more to determine what country you're really in to restrict certain features.
So it's not as simple as swapping your location in settings, or even traveling to somewhere in the EU, theres a certain sticky-ness to what your device thinks is your current country.
Edit: bit more info on eligibilityd here https://theapplewiki.com/wiki/Eligibility#eligibilityd