This is a pretty good read about why the NBA has found itself with such a lack of parity.
A select quote:
"Obviously, there are a limited number of superstar players in the league. How can you create parity when the acquisition of just one player can produce that many wins? Obviously, the teams with these players would have a great advantage and that’s the way it should be. If you get lucky and score a champion, well, then you win championships. What if you’re a bad team, though? How can you improve?
In a free market, the problem would resolve itself. Star players are a valuable commodity, so you’d have to pay a premium to get them. Buying a Lebron James would cost so much that the team might not be able to afford great players to surround him. Thus, a team without a star could stock up on solid players and compete with Lebron + Junk. Don’t have a superstar? Be smart, and you can still play deep into the playoffs or maybe even win (see 2004 Pistons, whose best player was a defensive specialist and best offensive player was named Chauncey).
By establishing a team cap, the only restriction would be that the huge market Lakers, Knicks, and Bulls couldn’t just drown the opposition. The cap prevents limitless spending, but teams were still forced to make decisions about how to build a team. The Lakers tried to make a “super team” in 2003-4 by acquiring Gary Payton and Karl Malone, but ended up having to play Deveon George for nearly 2000 minutes. Spend a lot on stars, and pay the consequences on the bench.
The individual cap is the root of most of the problems. By capping the total salary a single player can earn, the NBA has established an uneven market for wins. Superstars are severely undervalued. Players on rookie contracts are undervalued. Mid-level players are overvalued. It’s as simple as that."
So they established rules for trading that achieved just about the opposite of what they were meant to do (i.e. 'share the players', the explicit message of the CBA after the last lockout).
We as gamers of all people should know a thing or two about poorly thought out rules resulting in unintended consequences. 