The main issue? The owners desire to have the right of first refusal - also known as some serious restricted free agency.
The basics behind the right to first refusal? Basically, the owners want to have up to three players that they can essentially turn into restricted free agents by matching any offer that another team offers one of their free agents. So if Tom Brady becomes a free agent and receives an offer from the Houston Texans, the Patriots would have the option to match that offer and keep Tom Brady.
In that scenario, Brady wouldn't truly be a free agent because he can't go to where he wants. He essentially has no control over where he can sign because the Patriots would be crazy to let him go to another team.
This would also make teams not want to bid on certain players if they knew they had no chance at getting them. Would any team think they had a legitimate shot at Brady? Of course not. So why waste your time offering him a contract? This could drive down the market value of Brady and the Patriots could potentially get him for a cheaper price because there would be less offers for him.
This would be an awful thing for the players to agree to. The best players in the league could never become true free agents because they would have no control over where they can go. I don't blame the players for holding out on signing until this gets changed.
I want the lockout to end as much as anyone, but not under those terms. The owners already have the transition tag and franchise tag, and that should be enough.
We are almost there, we just have to get past this one last step.