I suppose there's just one Stonehenge for the same reason there's only one St Peter's Basilica, it was a lavish and expensive project for the time, bigger and better than had been seen before, more advanced in design.

Do you think stone circles are just interpretations of a common theme? Like modern churches, they all differ. Or did they serve different purposes, like arenas, churches, corales, etc?

The Rollrights is on the Jurassic way, which meets the Ridgeway down to Avebury so it could be plausible that the people who built Beltany could have been on a pilgramage to Avebury and built the Kings Men.