Although the BBs didn't state these reasons, the rules were put in place to eliminate "mono-monster" big men, as well as to thin out the player market as the BB userbase has been shrinking steadily for some time now (it's about 30% smaller than it was in 2010).
Anyways, if a player doesn't sell for 10x his salary, he's a poorly built player and he shouldn't be in the game. There are better ways to solve the problem of inefficient players dominating the sim, but the BBs went for the quick fix to avoid altering the sim, so whatever.