There's surprisingly little disagreement in the sports where strength is the key quality. There's argument about exercise selection and rotation, some dispute about programming and so forth. But everyone knows you need to frequently lift >85% of your 1RM, and everyone does.
However, the strength sports are different. Powerlifting requires training for maximum force production. Weightlifting requires training for rate of force production. Strongman requires training for strength endurance. These are three related but distinct physical qualities, and naturally, specialists in these sports train differently. To the amateur eye it can seem confusing and there's a temptation to declare that one of these is "best" and that other methods are dumb.
Otherwise, most of the fad arguments take place in bodybuilding, where the degree of physiological literacy is ... lower, on average.
Bodybuilding is also the only one that I don't really consider a "sport." It's a beauty contest. I think the prevalence of fads is higher because there's no objective performance metric.
While I share your suspicion that anything requiring judges to give a score is probably not a sport, if there's one thing bodybuilders and "fitness" models are masters at, it's manipulating water retention. They've got it down to a dangerously scary fine art.
... on the not-so-glorious side of the ledger, they probably know more about steroids than anyone short of an ex-East German sports scientist.
Actually, I think wrestlers may be just as good at manipulating water weight. The biggest difference being that wrestler have to compete soon after, and if they didn't cut properly, they'll become exhausted during their match and get mauled.
However, the strength sports are different. Powerlifting requires training for maximum force production. Weightlifting requires training for rate of force production. Strongman requires training for strength endurance. These are three related but distinct physical qualities, and naturally, specialists in these sports train differently. To the amateur eye it can seem confusing and there's a temptation to declare that one of these is "best" and that other methods are dumb.
Otherwise, most of the fad arguments take place in bodybuilding, where the degree of physiological literacy is ... lower, on average.