If you look at the extreme left hand side of this picture you'll see an opening. I'm guessing most or all of the ancient structures were built with water and this opening was part of the system to return water to a collection point.
I'm sticking my neck out here since I've not studied any of these other sites except cursorally.
But the point is at the corresponding points on G1 there are the boat pits. These could have been related to reducing the weight of the the loads in order to cushion the lift or fascilitate it.
Note too that the "ramps" that were used to build this pyramid might have been simply left in place.