While I agree with your premise as it follows scientific principles, the problem is that, in the case of Gundry, he's applying a narrow scope of medicine to everyone based on his own patients, which makes it anecdotal because you cannot apply a narrow scope of results to everyone. He also says things that are just plain dumb. Most of the ads I see with him in it are a mix of that narrow scope, facts and a dash of BS because he LOVES attention. That's why he wears colorful glasses frames (see Elton John and Liberace for more flamboyant examples).

In the case of the others, they mix truth and lies to get rich. Andrew Hubermann, for example, used to promote the truth but wasn't making much money. Now, he's lying frequently and making big money. That's what most of them do - they tell people what feeds their hopes and fears, a common tactic of con artists, mixing the truth and lies together so that people become dependent on them. A lot of people fall victim and give these scumbags their money and trust when all they deserve is prison.

It's not a matter of differences in biology; the core of what they're doing is conning people.