Funny how no one has come up with so much as a dropped tool, or a nut and bolt or an empty beer can of demonstrably alien origin.
Because of course we 21st-century human beings would easily recognize technological artifacts of a million-year-old civilization for what they are.
Seriously: What would Leonardo da Vinci have made of a solid-state circuitry? A flat-screen? How about a 24-inch cathode ray tube? What would he have made of them, even if they were still in pristine condition? Since he doesn't have a working electrical socket into which to plug them... And doesn't actually even understand the concept of "plus" pole and "negative" pole... And that's a technological gap of a mere 500 years. Now imagine: 500,000 years.
Clarke's 3rd Law:
Any sufficiently advanced technology is indistinguishable from magic.
Regards,