One theory is that because there's no private healthcare for some stuff e.g. A&E, in the UK, if you want good healthcare (as all the public healthcare is shit here), you're better off going elsewhere that has both decent private and public healthcare.
But also, property is expensive in the UK in the four cities that matter (London, Birmingham, Manchester, and Glasgow). $1M is £800k, given at most half one's wealth will go into one's property, you're looking at £400k. Compare what £400k gets you in those four UK cities, or even rural areas of the UK where it's still expensive, to anywhere else lol.
If I was a millionaire, I'd ditch this island lol.