It's just music. Seriously.
Music is a product, that in order to make money, must appeal the broadest common denominator. Before the age of piracy, certain niche genres like conscious rap, Jazz, the hardcore heavy metal genres, or adult contemporary could turn a profit because of sheer volume of the music sales market.
That's not possible now. Everything must sell a certain FIXED amount just to be profitable. Imagine the music market is a big pie with a very large "pop slice" and 100's of other smaller slices given to other genres. If every product has a certain FIXED sales volume in order to be profitable (not a pegged percentage) and that pie is shrinking on the order of 10 to 20% per year, then some of those slices are just going to be wiped out.
There isn't some nefarious objective going on here by anyone in government or industry. Whether you like it or not, the majority of people in the world don't like underground rap or conscious rap, in fact they find it to be boring.
OFWGKTA is cool, but will they ever have a youtube video with 200 million plus views like PSY, Lady gaga or Justin Bieber? No, they don't have that demographic appeal and neither does your favorite rapper. Deal with it.