Just another simple observatory, similar to dozens around the globe, made with clever artifice and ingenuity. And the reason always proffered for these unique astrological platforms? Why, so that the primitives would know the precise instant in which to drop a seed in a stick-scratched furrow in the ground. Yep, star alignments, geophysical constructs, and enduring monuments all brought together for the simple folk to plant some crops.
Despite the wonderful arguments for such an august objective, wouldn't a couple of sticks in the ground have sufficed, or a stone on the ground that captured a shadow of another edifice twice a year have been sufficient?
Maybe I'm jaded, but that seems to evince a lot of brain power for crop planting, evincing a tad bit of overkill to farm and till and harvest a field.
HA! No, I don't think you are jaded. Some of things seem to be WAAAAAY over analyzed, and ignore that would have been obvious to the locals at that time..
We are in the prenumbra of the finest shaved edge on the very tip of the pinnacle of cultural and technological achievement of mankind from appearance on the Earth to dissappearance from the Earth. To suggest that a period of history deemed "primitive" could have had advanced tools made for advanced purposes from advanced motivations and planning upsets the sacred curve of developement and is considered among the most abysmal of heresies imaginable. 
A book I've read about the Great Pyramids and many lessor ones is that they were convenient surveying markers for redrawing property lines after the Nile floods. They could be seen for miles and that so long as any two pyramids could be seen, you could triangulate your on position, etc.