Its marketing 101. Everybody wants to see beautiful young women perform. Young girls, young boys, old men, everybody. We would all rather watch an attractive young women than an old guy if given the opportunity. There are literally millions of singers in the world better than Katy Perry or Taylor Swift, but very few of them are as marketable. In todays music world the image is more important than the substance. Its not good, its not bad, it just is. If you think this kind of thing is not discussed in every board room of every corporation everyday you are delusional. I applaud the people who can put it all together and market themselves in a profitable way. I wish I could make money from youtube videos, but nobody wants to see another middle aged guy play the drums. The market is already saturated.
Its not sexist to say that people enjoy watching her because she is an attractive young woman. I am not even sure that is debatable, reading the comments in her videos leads me to believe is damn near a fact. It would be sexist to say that she cant play the drums because she is a girl, and I have not heard anybody say that here. The horse might be dead on this subject, but its always worthwhile to give it a good flogging once in a while for good measure.