Understanding fighting =/= understanding how to judge without bias.
Fighters are the least reliable source for unbiased scores on fights. Everyone has ties to everyone with camps, friendships and rivalries. Not to mention scoring philosophies that have ties to their own in-octagon performances. It's the same reason why you don't poll NFL players to find out who belongs in the Hall of Fame -- it's largely the media's job to determine those things. The same goes for pretty much every other major sport.
That isn't to say the media doesn't form relationships -- in fact it's an integral part of being a good journalist to do that -- but it's a work relationship first and foremost.
The media also follows the sport more closely than most professional athletes do in their respective sports. Anyone with any experience in the media or in professional sports can attest to that.