The similaritites in architecture are all physics related. “This works and this here does not”.
The other similarities are common to other cultures.
As far as early colonization of the Americas, I suspect that most of the evidence is under the water of the continental shelf. The seas rose and fell a good amount during the last 200,000 years or so.
I totally agree. I wonder what is hidden under the mud of the Missippi delta. The delta would have had a mild, favorable climate during the last ice age and would have been a natural location for a villages and cities. When the last ice age ended 9000 years ago the sea levels rose 300 feet and the Mississippi River would have covered them in sediment.