My highly educated guess: one of them is the owners continuing to come down significantly from their original demand of taking another $1 billion off the top of player earnings. The players always believed this was an outrageous demand and the players were right.
Meanwhile, lawyers for the two sides appeared in St. Louis today before the Eighth Circuit to argue the validity of the lockout. According to Andrew Brandt, the tenor of the hearing was a direct contrast to that which was presided over by Judge Susan Nelson and resulted in the lockout injunction. Brandt writes that the two Republican-leaning judges appeared to be "empathetic to the Owners' argument" and expects they'll rule in the league's favor.
According to Mark Maske of the Washington Post, Kermit Bye - the lone judge who dissented from his colleague's stay of the lockout - told the two sides at the conclusion of the hearing,
We will take this case and render a decision in due course. We won’t, I might also say, be all that hurt that you’re leaving us out if you should go out and settle the case. But that’s up to you. But we will keep with our business and if that ends up with a decision it’s probably something both sides are not going to like but at least it will be a decision.