Disclaimer: By no means am I an expert on the subject, but as a peoples watcher, I got to say that this stuff gets me going.

That being said, a lot of the attention they're getting is due to their current work/drama. Take someone like Kim Kardashian: she makes her living off having her name out there, and she does it in a rather explicit way.

Going back to the rappers. A lot of the "oldschool" generation (as I would consider it), love Eminem because he didn't conform to mainstream (in the early days). He genuinely expresses himself all while expressing his inner-genius and capabilities. I can't think of words to describe his manner. His lyrics, in other words, comes from within, they are real experiences that adds up to who he is today. So, on the other hand, Kanye West is a bit more mainstream; he raps, but he goes into the Pop industry as well. Same with Iggy Azalea; they both are able to fit into more genres.

Iggy Azalea has attractive features that make her look on the front of pages. By no means do I think she's perfect (vocally), but she tries and you can hear it when she's singing/rapping. There's a very serious attitude in all of it.

Kanye vs. Kendrick....I wouldn't say good example here. Anyhow, Kanye has an education, yes, but in the end these people are on a equal front. It's like comparing Tech. Companies. The public doesn't know that Google's business model is on a polar opposite than say, Uber. In the end, it crunches down to numbers. Numbers is what makes an artist popular. If you have money, you have ads. The more you hype something up, the more people will get into it.

TL;DR: They're on a equal front, numbers matter the most. Some people flaunt their body parts to get somewhere, and women are luckier than men in that category. Some people express their lives and a more personal connection than those who are versatile to fit across genres.