Partial Source: Pwinsider.com
The big reason that Dolph Ziggler is back in the midcard position after his brief World Heavyweight title run is that he reportedly has a bad attitude around other superstars and media. WWE is not happy with how he represents himself both within the company and during media appearances.
Ziggler has claimed that he's just working his gimmick and has the same attitude he would with storylines, but WWE doesn't buy that. He doesn't have a lot of backing with officials because of how he speaks to them.