In the first place, so much of the aesthetic is based on gangster culture. Black gangster culture specifically. Based off of the actual real problem of black violent gang culture . How can that be considered good in any way?. And the music itself is low class, simplistic and has no real melody. i don't know why anyone likes it to be honest.
And White or Asian people copying it are worshipping black gangster culture because so much of hiphop and rap is based around that. Just look at the lyrics and music videos and what the "singers" wear and how they conduct themselves. All the tattoos , too many metal piercings, stupid amounts of jewelry (again , its based off of materialistic gang culture) just all around uglyness , rude gestures and behaviors, trashy . In general its all just vulgar.
And why is something that was invented decades ago always promoted like its "cool and modern"?
Another point is, although not new, it is comparatively new. It is one of the newer forms of music, so there is some innovation going on, just not so much in the mainstream which, as has been mentioned, promotes the cancer. But it is cool that you can be there to see some new things, or find the older stuff that was super innovative. You can find innovation in any style, but there might be more of it going on in rap, because it is newer.
Rap Phenomena (1981), some of the first rap from Japan.
Not to mention the heavy emphasis on lyrics over sound means that the innovations are more likely to come from the same places that poetry did.
Where everyone treats the move from iambic pentameter and other forms of rhythm to "he just said words that don't rhyme, but put line breaks are certain spots" is treated as revolutionary and genre defining.