User blog comment:ArtDraw12/TD Theories: Why DJ didn't just quit?/@comment-2066983-20160829013418/@comment-11883116-20160829014035

As I said it could also fit in-universe reason if the contract said they can't quit more than once in the series (or in two seasons in a row, as you said). Too bad it was never revealed if their contract actually says so. It'd make much more sense this way.