Hip hop/dance music is mostly producer and engineer's music. They have so much to do with the final product it tends to eclipse the recording artist's input (even when the latter has a songwriting credit).
This, by itself, does not disqualify a track from being musical, but it is a different set of talents, and I think (my experience anyway) that is one of the driving factors behind a general distrust/dislike of these genres.
Some might even argue that producers and engineers are in the drivers seat because the number of musicians (by conventional definition) is decreasing, or possibly that it is so difficult to master an instrument.
I'd argue that the challenge of mastering an instrument is part of the fun - but that is a separate topic.
There are good, and bad, examples of music in every genre. At least to the extent that one can judge these things.
Then there are tracks that offend a large (and vociferous) portion of the population. When I was a lad it was rock and roll, today it is HipHop and Rap and related styles.
Do these style offend to protest, or offend for the fun of it? Does it matter.
The one big difference - to me - is that while my buddies and I were "studying" rock and roll we were also studying the classics, and jazz/big band, and even film music. Today that seems to be changing. If I really were a curmudgeon (wait, am I?) I'd suggest a certain laziness on the part of the students.
And when I say studying rock and roll I am only half joking - while we had the Mickey Baker and Joe Pass books for jazz we had "Live at the Filmore", "4 Way Street" and too many others to mention for the rest of our studies. I mention those two because my friends and I spent countless hours dissecting them.