Well I don't know. Lets look at it. If an advanced culture existed for arguments sake, then yes, they would leave things behind for sure, and to be sure, as rare as this civilization would be, its artifacts would surely stand out as curious mysteries to all following civilizations to come. So lets presume some hypothetically highly advanced civilization existed way back and of course did leave tones of things behind as artifacts showing this.
We can at least agree that there is ample evidence of low tech hunters and gatherers during several periods beyond 10,000 years back, and there is some evidence that the farther back you go, the more rudimentary were the examples of their organization, tools, etc.
Wouldn't these less advanced cultures that followed, for which there is infinitely more evidence, have taken control of, fought over, and eventually destroyed a lot of it? Wouldn't religious leaders either make power plays to control all of these artifacts of technology and hence create an environment of coveting that would eventually lead to their destruction from spite or jealousy, OR, perhaps couldn't they have seen these odd relics of high tech past scare them into demonizing them and demand their destruction?
These things are possible of course. The question is, how much evidence on the surface and visible over the past tens of thousands of years would have succumb to this fate? Do you think a coke can would have just sat there in the dirt and not got picked up placed on a purple velvet pillow and prayed to until that civilization was overthrown by the next who then mounted the coke can on the "Staff of the Gods" for the next 300 years, and so on. Wouldn't any of this odd out of place technology be considered objects that once belonged to "THE GODS" and therefore be scoured and gathered and controlled?
Believe me, it bothers me that there's no evidence of that advanced culture. It bothers me that it actually makes sense to me that were there evidence found in the past of this kind of thing, that it should be kept from public consumption for fear of a terrifying meltdown of the vast majority of the planets religious beliefs. And this fact supports the suspicion that there might be some artifacts in existence, and in the same breath provides a reason why we haven't seen it.
But I bring up the above to at least assist in the rationalization as to how its been missed to date. Maybe these artifacts are just really hard to find now. All I can suggest is that with the exponential expansion of the pace of information exchange, that old control system is bound to fail and I think we are the fortunate ones who will see the first cracks and exposures of the truth. Exciting times.