Only recently there is growing evidence that there are ancient artifacts made with precisions/symmetry/accuracy that could only have been approached in the last 50 years.

https://www.youtube.com/watch?v=WAyQQRNoQaE

That doesn't explain what happened to the tools, but that might be attributable to rust, death of small numbers of experts by war/famine/cataclysm/disease, and widespread recycling of rare metals and objects. OOP artifact-finders have traditionally been mocked into silence. It was 50 years before Antikythera got serious study, 50 more before it got close attention.