it's not because they just haven't tried your favorite diet.

This seems somewhat unfair. There are a handful of diets that work on a broad variety of people, such that the prior any one will work for a particular person is higher than a novel diet like Shangri-La. And so unless you've tried slow carb/ketogenic, intermittent fasting, 30g of protein for breakfast, and ECA stacks and none of them worked, it seems like you're updating too far in the direction of "all diets don't work for me" from the evidence that "diet X didn't work for me."

(The only one of those I've tried is IF. It worked for me.)

The world is full of metabolic diversity. The fortunate who do not appreciate this are the metabolically privileged. That they can lose weight with an effort causes them to be unfortunately deluded about what is going on.

What's the difference between this and the claim that you are a metabolic mutant?