Another explanation is that these and similar sites such as Stonehendge, the Egyptian pyramids, Mayan temples etc. are boondoggles. Financed by the local rulers to keep their subjects occupied so they don't ferment revolution. Generally the local oligarchy will have concocted some type of mumbo jumbo to justify their social position and then they finance public works to get as many people as possible complicit in maintaining the ideology which underpins the status quo. This is why it is difficult to find evidence of slave labour on these sites, it would be hard for an ideology to survive for very long if it's monuments and places of worship were built and maintained by coercion.
Something is not right. This message is just to keep things from messing up down the road