Health in general has always worked like this, from supplements, to organic food, to avoiding ultra-processed foods, to gluten-free diets, pretty much every popular health fad has no provable causative effect on health.

Most of human behavior is irrational. If we were all perfectly rational, we would have healthy diet and exercise habits from the get go, and we'd have plenty of time to prepare food and exercise, because we wouldn't waste any time on entertainment.

>pretty much every popular health fad has no provable causative effect on health.

Isn't this almost true by definition? If it actually works, it's not a "fad", just "science" or whatever. Advice like "eat more vegetables" and "don't drink alcohol" probably do work, but they're ingrained enough that nobody thinks they're "fads".