Just a joke, I think. He's done this in at least a dozen countries. I believe that includes several separate "events" in the US.
One might suppose he didn't think naked Brits would be as "artsy" as all those others who went before?
Or maybe he thought his "work" wouldn't accepted there - and was afraid?
When I first heard of him, I would have assumed he'd have gone where people had the most beautiful naked bodies - but having seen some of his work I'm quite sure that's not among his criteria. It looks more like it's wherever he can get by with it and can gather enough "sponsors."
Maybe he just ran out of gullible fools in the less civilized countries and decided to "try the harder ones."