We lose technology all the time, we can't figure out how they constructed those sky rise cathedrals either, turns out a plague killed most of the engineers so we can't just reproduce it anymore, it's lost, same with technology that got us to the moon, it's lost, and we did in such a hurry and re used the parts but the original technology belonged to certain men who were rushed and was not wealthy enough to produce another one so there you go.. likewise with the pyramids and other structures, which turn out to be older than what we were taught.. The ancient Egyptians also wondered about the ancient Egyptians, the pottery is found to be so precise and beautifully crafted for an ancient civilization yet there are crude writings scribbled on it suggesting that whoever wrote their name in it was just taking credit for it :/
As for the ancient astronaut theory, especially the Annunaki stuff is just babylon mythos who believed in telling stories through the stars but Sitchen took them "literally" and made good living off of it