Another part is that like pop, rap is full of people who are legitimately not talented and just collecting checks. Some of the music is so disposable, no lacking of artistic merit, so trash that I understand why some people associate "rap" with that. A person probably wouldn't exclusively associate "rock" with trash like nu metal for instance. And of course even trash rock can get props solely because someone is playing an instrument (oohhhhhhhhhh).
The funniest thing is cacs who truly think Eminem is the only talented rapper, and the only "musician" in rap "because he makes beats and raps!" Sometimes I wish I was a 5%er yall.