I don't think you're right on that.
What the NBA can't do, however, is use the recordings in any court proceeding, and that would prevent the NBA from providing evidence for the decisions that it made. That would present a conundrum to the NBA's lawyers.
Again, yes they can. But even if you were correct, the NBA wouldn't need them. They can claim that Sterling was responsible for loss of revenue, loss of sponsors, discord with the players, and any number of other things that were not in the best interest of the association. The NBA constitution gives the commissioner the power to impose the lifetime ban and the $2 million fine for that alone.
...or to communicate in any way, any information so obtained, or who aids, agrees with, employs, or conspires with any person or persons to unlawfully do, or permit, or cause to be done any of the acts or things mentioned above in this section, is punishable by a fine not exceeding two thousand five hundred dollars ($2,500), or by imprisonment in the county jail not exceeding one year,
This appears to make it illegal to disseminate the illegally obtained recording, by my reading of it. TMZ broadcasting it would be "communicating" it. The DA is probably not keen to go after a broadcaster, especially to defend Sterling's rights, but that does not make it legal. It's more like Obama refusing to enforce immigration laws.
They can claim that Sterling was responsible for loss of revenue, loss of sponsors, discord with the players, and any number of other things that were not in the best interest of the association.
Sterling didn't do or say anything that they can introduce into evidence to prove that he is responsible for the loss of revenue, sponsors, etc. He hasn't committed any "conduct" that the NBA can legally prove, and it is conduct of some kind that the NBA must show. The NBA has what is known as a proof problem. They can't connect the dots without evidence that is inadmissible. And that is the conundrum. I suggest that those who want to really delve into this issue read up on rules of evidence and trial practice.