We have tools that don't require us to find sites that may have been destroyed. For one, genetic studies constrain human population levels assuming any descenda

We have tools that don't require us to find sites that may have been destroyed. For one, genetic studies constrain human population levels assuming any descendants were related to either living people or sampled remains. That constrains population levels quite a bit. Moreover, we can roughly track human habitation on landscapes by how much fire they used as well as changes in flora and fauna. Recent results have even demonstrated direct detection of ancient humans from environmental DNA they left behind in skin cells and such, but that's quite new. All of these different lines of evidence greatly constrain the types of 'civilizations' that were possible to highly localized ones with small populations, or that were completely and utterly wiped out with no surviving material culture, technology, or descendants. That's to say it's not impossible, but highly unlikely. Any explanations all those lines would have to be parsimonious and no one's brought forth good evidence for such a narrative.