Total hypothesis, but maybe the folk of the Preselli's moved to the Wiltshire plains region, up sticks and took their monument with em'. Elite priest class? Better stone masons?, better farmers? nosey bastards? who can say. Absolutely no evidence for this idea, pure fantasy, but then again, with prehistory there are no absolutes. One week it's he says, the next she says. Also, just cos' one region is wilder than another doesn't automatically mean that folk are living there just cos' a monument or two may be plonked on top of a notable/ noticable hill. After all, you don't really want live where there isn't game, fishing or foraging, you want your folks to be able to eat. I can't say why those megalithic builder decided to drag a selection of stones a hundred miles or more, but all I can say is, it's still a region on the margins of Britain. It takes a good while, even in a car to get there, ditto Norfolk/Suffolk. Maybe these folks brought something to the tabled the dwellers of central Britain hadn't thought about.

Either way, I still think it's an exciting find, pour as much cold water on it as ya like :)