Basically, the financial structure of the league as it currently exists doesn't work. Depending on who you believe, roughly 2/3 of the team's lost money last year.
It's frustrating b/c, really, it's on the owners for being idiots. There were a ton of players who got really long contracts with completely ridiculous salaries. Imagine if a club like Wolves decided to sign Kevin Doyle to a six year contract with him on 150,000 a week. Now imagine if everyone else in the Prem was doing the same thing. Financial structure would fall apart overnight. So player salaries are the main cause of the issue, but I don't really blame the players there. If someone offers you stupid money are you supposed to turn it down because you're not worth that much?
If you want a more thorough breakdown on it, you won't do better than Bill Simmons on Grantland (Simmons, I might add, is a Spurs supporter).
Simmons' sums it up on Twitter.
If I Ruled the (NBA) World
Dizzying Heights and Terrifying Lows
A Fan Friendly Solution to Fix the NBA
(I'd also hazard a guess that BlueCrewLA could probably make a few interesting observations on this issue since he's one of the sports & finance gurus around here...)