There are currently no details on what caused the downfall of Cody "Stardust" Rhodes and Goldust which may explain why the two half-brothers haven't been utilized much on television in recent weeks.
However, one possible reason may be the fact that there has been some bad blood between WWE Management and their father, WWE Hall of Famer Dusty Rhodes may have possibility derailed the Rhodes Brothers' push as explained below:
We noted earlier that Dusty Rhodes, who has been working in WWE developmental for some time, gave Prince Devitt a tour of the Performance Center when Devitt arrived in Orlando. It’s said that Dusty’s responsibilities in NXT have diminished over the past few years as his health has worsened. Dusty did lose a lot of weight but reportedly underwent double hernia surgery recently.
It’s been reported how Dusty got major heat on himself for putting his hand in Stephanie McMahon’s face during an in-ring segment on the September 30th, 2013 RAW. Dusty has been in a bad position politically since then. It was said that Rhodes has been frustrated with his part time role and he’s talked about retiring sometime next year.