The island is tiny, and only has about half a dozen houses on it. The visitors are there because it’s a nature reserve, so generally don’t want to be on their phones anyway. It’s not worth setting up a relay station over just telling everyone before they get there.
It’s weird they wouldn’t work with a UK based telco to set up a relay station explicitly to prevent this.
Why prevent it, when you can just shrug your shoulders and rake in the money?
The telco likely doesnt make any extra from the roaming, they very likely pay it all out to the company the roaming took place on.
The island is tiny, and only has about half a dozen houses on it. The visitors are there because it’s a nature reserve, so generally don’t want to be on their phones anyway. It’s not worth setting up a relay station over just telling everyone before they get there.