Blame Rap music. Rap music and the culture overtook R&B's market. It's much more attractive to be edgy, rough or in some cases mildly retarded than it is to sing a song that has a good melody and purpose. That's considered soft. That's why R&B singers make rap/hip hop oriented music so they can sell.
It's even in the lyrics as well. Chris Brown's sex you back to sleep song is one of my favorite songs from him because it's a true R&B song that has that real R&B feel. Then I heard the uncensored version and I was disgusted. It was basically hip hop language in an R&B song and that doesn't go together.
Luckily for me my iPod is strictly R&B and most of it is older R&B.