Its a negotiation. Of course one side views the other gain as their loss. The key is to allow the other side to think its getting a big win when its really getting less than it thinks.
In this case the question is who got greedy? The original story was that the NFLPA wanted a concession for agreeing. But I never heard what that concession was. The only specific is a the League request you mention about practice rules. But was that the original bone of contention or was it a counter offer?