You are missing the fact that these are businesses first and foremost. Might as well ask "Why can't more prizefighter fight for cheap so they can put more good fights on one card and make fans happy!!"
Sometimes I think that the powers that be in boxing are trying everything to make the sport as unpopular as they can and this is just one of those things.
I stuck this at the end of a long post so might be worth re-posting. Gives the idea that the rights to fights are owned by multiple entities, complicating their re-use. Yep, they should figure that **** out. One more way in which the sport shoots itself in the foot. http://sports.espn.go.com/sports/box...ory?id=3390712