Thing is, he's not really pointing an unexplained mystery.

We know 90% of about how a lot of these sites were built and a good chunk of their history. Some of the older/more recently discovered ones such as Gobleki Tepe, obviously less but still a fair bit. Claiming that Mesoamerican and Asian megalith sites are aliens/Atlanteans isn't really helping work out that last 10%.

Pointing at what science has proven again and again to be a natural rock formation 25m under the water and claiming it's the remains of Atlantean civilisation doesn't advance much either, after all it's been proven wrong before.

Meanwhile, ever since Europe was disproven to be the birthplace of modern humans in the 19th and early 20th centuries, people have suddenly been coming up with all sorts of reasons why non-White folks sites weren't made by locals.

I will give Hancock credit that I don't think he is actively racist, as he does correct himself when he implies that the locals wouldn't have been able to do things like stack rocks.