The inverse of broad appeal is the concept of The Long Tail, where there's a vast array of niche artists, that appeal to a small number of people.
https://en.wikipedia.org/wiki/Long_Tail
There's a book by the same title, written by Chris Anderson:
http://www.thelongtail.com
Prior to the internet, when advertising and media outlets were centralized, and retail businesses were distributed geographically, it was very difficult to gain a large following with niche appeal. But now that the internet has inverted the scenario, with decentralized, global exposure, and centralized market places like ebay and amazon, niche artists have a fighting chance at becoming famous within their genre.
In other words, it used to be that the only way to catch some exposure was to appeal to centralized broadcasting networks, and they only took chances on performers who were low risk. Now, with the internet, risk doesn't really matter, and mass appeal is literally measured by the size of your following. The larger your following is, by default, the more compromises you'll have made to appeal to everyone following you.
If you capture 1/2 the world as your audience, then you appeal to a broader, and more diverse audience, which has less in common with each other member of your audience, than if you managed to capture 1/4 the world. Getting half the world to agree on something, as opposed to creating something that three quarters of the world cannot relate to.
So, Aesop Rock raps about hating your boss, and many people say: "Gee, yeah, I hate my boss too! This guy's awesome!", but Kool Keith raps about Kenworths with wings, and lots of people are like: "Is he weird?" because lowest common denominator.