it’s really quite silly, as others have pointed out, because so much “Jewish” music has been derived from goyish music.
These are people in it for the power and control. Religion is a power much like political office in its potential for abuse.
Incidentally, I stiill remember in high school a classmate was yelled at for listening to (relatively benign) non-Jewish music during sefira. The student replied “but rebbe, you said this is garbage, not music!”