The “elites” in every culture kept many advanced techniques / knowledge to themselves. How else could they separate themselves from the peasants?
Many people died as a result of their “experiments”
Someone had to taste the unknown berry on a bush and it was for certain it was the elites.
Still others were sacrificed to their “gods”
Many cultures built giant stone structures..nearly all of them have to shown to be a result of leverage or some other reasonable technique. Still, they were quite clever.
They built mechanical devices that compared to today’s technology were little more than coin operated music boxes. But to the average villager they seemed like magic or inspired.
As for their knowledge of the stars and the seasons..they spent a large part of their lives outside observing and marking events.
They observed that the sun was at a certain point in the sky every year and built observatories for such events.
Yes, that's the standard hypothesis, but no one in the modern era has been able to duplicate such feats of engineering - though it's been tried many times.
Consider this. The 'trilithon' foundation stones of the Temple of Jupiter in Baalbek, Lebanon weigh 800 tons apiece, and an unused block in the quarry nearby weighs in at 1,200 tons.
The obvious question is, how were such megalithic stones quarried, dressed, then moved and set into place by the ancients, who didn't have access to the technology required to accomplish such a feat. We can't do it ourselves, even with the best of our modern technology.
As I said, skeptics will adamantly insist that it was done with simple stone implements, leverage, and tremendous amounts of manpower, but that's never been more than an assertion. It's never been proven, though it has been tried.
The fact remains, though, these inexplicable monuments are there, and someone obviously did have the tools and technology to put them there.
I believe we err when we attribute their building to the ancient humans of our own recorded history. I believe the simple answer is that they were built by an earlier, high tech society that was wiped from the earth by some major cataclysm tens of thousands of years ago. Time obliterated all traces of these people, except for the megalithic stone structures they left behind.