As WT had tried to point out...if significant portions of either airline have to be divested--particularly, if those portions end up going to a competitor--the merger no longer makes economic/financial sense. AA, as is, is already number 3. Why ever would they do a merger where they ended up #4? And, why bother if, after the merger, you are still #3?
And, you keep forgetting that regardless of what one DOJ official says, the court documents are directed at the anti-competitive statements made by airline executives. No amount of divestiture can fix that.