Well, yes, it is a fad, I suppose. However, this fad has lasted at least 30 years so far. How long does it take a fad to grow up?
Difficult to say. Some people actually still think that serious forms of expression include rap.
My aunt was sold a Jack Lalane juicer back in 1964 (hardly used it, lived to 95). People then were actually juicing fresh grass clippings for the chlorophyll. The juice fad goes way back.
For me, there’s nothing like juicing whole limes for daiquiris (using our 50 hp Vitamix). And shedding the blood of the grape is a daily ritual.