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")
In the last 30 years, only eight teams have won a title. Seven teams combined for 29/30 of those. The same teams are winning over and over and over. So examining the last ten years is meaningless when that is what's happening, you'll get a false sense of parity by seeing it shared among six teams in ten years (as though six different teams win every decade).
The bottom 15 to 20 teams in the NBA can never, and will never win a title under any circumstances. There is zero competitive parity. In 30 years, only one team has won a solo stand-out title, and that's the Dallas Mavericks.
One other problem with this article, they say that U.S. sports gambling has been estimated at $800 billion (it hasn't), and then they link to an article that doesn't say that at all. That number doesn't even come close to passing a common-sense test. The link is referring to world-wide sports gambling.