They have a longer chronology of course, but could there have been more people? The population estimates have been drifting upwards for years.
I see an economy that can build henges as well organised and wealthy. clearly they were able to devote significant amounts of effort to henge building - I see them taking months not years though. In the case of Thornborough we have the same type of construction spread over twenty miles or so - clearly a well organised group of people building to a common plan.