Japanese Music

So I had a random thought while listening to some of my favorite Japanese artists and I find it kind of weird that a lot of places seem to label a lot of Japanese music as simply Jpop, Jrock, etc…. While I understand it differentiates Japanese music from say American music. I find it interesting that some artists, say if they were simply an American artist, would be hip-hop, R&B, metal, or whatever genre or even set of sub-genres you can think of. An example would be one of my favorite artists Shota Shimizu, who was labeled Jpop. I was thinking, if I were to randomly encounter him with no knowledge of who he was, I would have said “He falls in the category of R&B”. This question may seem random, or even kind of nit-picky, but I wonder what your thoughts are.