I've said it once in the Hip Hop class that I teach @ Temple University and I'll say it again, it all has to do with the fickle fans. NY was always the mecca for true MC's with lyrical dexterity, cadence, flow etc. The rest of the country, in part, just didn't have the feel of true HIP HOP with powerfull MC's with different feels (not cookie cutter). But as time went on, more people from other regions of the country got into the game and fans from other parts of the country embraced those artists from there region, even if the sound and lyrics were trash, elementary at best.
The fans dictate who is hot (sales, fame etc). If someone came out in a monkey suit with a banana mic, spitting garbage, but it was embraced for being different, that person becomes a star with little or no talent. Then you'll have copy catters that will do the same thing but with a twist and he/she will be the next star. The bottom line is that the fans LOVE a gimmick, not necessarily talent. Look at all the talentless people today in reality tv, other genres of music, entertainment etc. The world is getting dummied down and it will only get worse.
When anything moves away from it's origin, in many cases it gets watered down or weaker. That how I see Hip Hop today. As a DJ and Producer, I've grown weary of how the industry has become so one demensional. The sound seems all the same and the microwave artists have NO longevity because the talent is lacking. Nas once said "Hip Hop is dead", but I believe it's alive and kicking it's just underground now. The new phrase should be the "radio is dead!!!"