#2 Dean Ambrose ran his course in the WWE

Dean Ambrose and Jon Moxley are characters played by a man known as Jonathan Good. Before coming to WWE, Dean Ambrose made a name for himself as Jon Moxley.
Over the years the character of Ambrose has won every title there is to win in the WWE. He has been a face as well as a heel on multiple occasions and has feuded with almost every big star that can be named.
The character of Ambrose was done in WWE a long time ago, but the company just dragged it out for too long. If Jonathan Good wants to be remembered in history as Jon Moxley and not as Dean Ambrose, then the only place he can make that happen is WWE.
#1 More creative freedom

One of the major reasons that resulted in the departure of Dean Ambrose from the WWE was the poor direction his character was given after turning heel. His feud with Seth Rollins was good, but after their feud, he had fallen into the mid-card.
If WWE is serious about having him back in the company, then they should offer Moxley more creative freedom with his character and some input in storylines.
Jon Moxley thrives on hardcore wrestling so if WWE gives him the right amount of creative freedom, then he can do some great things within the company.