Note that a lot of professional-archeologist or professional-historian beliefs are also turning out to be false over the decades. Population-genomics is dispelling many commonly held beliefs of the field.

Professionals hate people like him, because he uses the exact same techniques as these professionals to extrapolate towards obviously false conclusions. It puts the professionals in an awkward space, as they have to start with accepting that their own field is based on a lot of conjecture, and that it facilitates this kind of fictionalizing.

This kind of fictionalizing was particularly true with non-western history of ancient civilizations where accounts were less dense, worse translated, had worse cultural context and dated back a few millennia. A lot of professional historians and archeologists have taken great liberty in interpreting the history of these regions, and the liberty taken by folks like Graham Hancock exposes some of these historians for the obvious 'fiction' that they stake their own careers on.

In that sense, ancient History & Archeology is going through a similar moment as cooking did a while back. Popular FACTS such as 'Marination leads to flavor penetration' or 'searing traps the juices' have now been thoroughly debunked. Food Science exposed the 'old wives tale' aspect of cooking, and now Population Genomics is spearheading a similar disruption within academic history and archeology.

The response to such an existential threat to the field is gatekeeping and defensiveness. And when a piece of work holds a mirror up to your field so brazenly, it receives the sharpest response.