Lopez has seen his role diminish with the Bulls as they start to develop their younger players. He wants out but the Bulls aren't going to walk away unless they also benefit.
The only thing holding back the Bulls is Lopez's contract. He is still owed $14.3 million and the Bulls don't want to pay him all of it. Lopez has to take a portion of what he is owed if he wants to be released. The Bulls want to recuperate their loss and only then will they release him.
As it stands right now, Lopez will join the Warriors. I expect him to come to an agreement with the Bulls because he doesn't want to be there. He wants to play for a team that will give him minutes. And he will be competing for an NBA Finals trophy.
Golden State needs a center badly and while DeMarcus Cousins will be returning soon, they still want Lopez as a role player. He is better than what the Warriors currently have and will be essential in making a run to the NBA Finals.
Will the Bulls help the Warriors get better? That is yet to be determined but it looks like they unintentionally will be aiding the Warriors they they like it or not.