I think they're popular because we are an industry of people that are very insecure. Lots of the guys with the biggest egos are the ones who secretly are the most fragile. I remember a time where I was in a club with another pro guy, and we were pretty trashed. He looks over at me and says, "Do I look alright?". I was like yeah, sure, whatever. And he continued to ask, "But like good looking? Chicks would like me?". To this I didn't really know what to say, so I was like yeah sure. Throughout the night, as he got more messed up he asked other strange similar questions. The guy definitely isn't gay, or at least has never showed any sign I've ever witnessed, and if I gave you a name, you'd be shocked.
I tell that story because outwardly this is one of the more confident cocky sounding/looking guys holding a pro card, but in reality he needed me to tell him he looked good at a night club. Lol. Imagine how insecure he must be before he gets onstage, or when he looks in the mirror as he's dieting. I think guys use gurus now to take that insecurity out of the equation to some degree. If they believe in the guru and their rep, it's a lot easier for many than believing in ones self.
I also think the media gives the gurus so much attention and props, that this has literally become the age of the guru. What the media and the fans don't realize is these guys don't do the work, they don't eat the food, and the definitely don't do the cardio. If they get credit, it should only be for the finishing touch they add (or sometimes subtract).