Only 7 teams have not been to the finals. That's not awful.
Only 7 teams have not been to the finals. That's not awful.
Compare it to the NFL of the last 30 years. 16 individual teams have won Super Bowls during that time.
Or compare it to the MLB. 17 teams have won the World Series in 30 years.
That 30 years represents the modern NBA, since the merger, Magic and Bird sent ratings soaring, and Jordan + the rise of global media changed everything about the league.
Now you've got Chris Paul shuttled off to LA in a market-stuffing trade, you've got star players like Melo eager to join up with dynasties like the Heat, and other players like Kevin Love that can't get out of the backwater fast enough. They all know how the league works now.
15 seasons not in the playoffs is bad, though, (14/30)^15 is about 1:100,000.
A model that introduces some correlation between the performance in year X and that in year X+1 without the need of a cartel could easily increase that probability, though.
For example, one could postulate that a team's quality increases with the qualities of its players and with the time they have been playing together ("you cannot buy a winning team")