“That is a poor analogy because we can indeed reproduce these works of art.”
Yes, but we don’t really do it with any regularity. What would get preserved in the archaeological record would be the kind of art of we produce the most commonly, which would be considerably cruder. So someone viewing our culture thousands of years in the future might surmise, just like you are doing, that we somehow mysteriously lost the capacity, in just a few hundred years, to create that kind of art.
I sure would like to see you prove that.