These things come and go in cycles. The fact is that building muscle depends as much if not more on endocrine status (which in turn depends on genetics, diet and other environmental factors) as on training. Thus, any training modality attempted by young men with hormonal profiles and general health of elderly cancer patients will eventually be discovered to "not work", making a way for a next generation of fitness influencers (or even the very same people who have also pushed the previous "only true way") to promote the next big thing. Influencers who, due to any combination of nature, nurture and trenbolone can get muscular by doing any kind of training.
The "one set to failure" style has also an advantage of requiring much less in terms of time and mental effort while still making people feel they are working very hard. "How can I progress if I don't constantly push my limits?" is a common reasoning failure that carries many different fitness concepts (not only HIT, but also HIIT, Crossfit and Starting Strength, to name a few).
Then there's Mike Mentzer's iconic status. He's one of the best known bodybuilders of all time, and he had some peculiar political and philosophical views. Coupled with his notorious feud with Arnold Schwarzenegger, and the fact that young people tend to remember the latter more as the Mouth of Sauron rather than a bodybuilder, it's easy to portray Mentzer as an embattled dissident repressed by the establishment for his great discoveries.
And for the benefits of training one set to failure, well, Pavel has exhaustively debunked that over twenty years ago.
