They are keeping Nate Diaz on the hook but not offering him a (realistic) fight in order to make sure he's under contract for a trilogy fight with Conor McGregor, who is still many months from returning. He refers to Andrei Arlovski going through the same ordeal at UFC 68-70.
The UFC ain't gonna let Nate Diaz walk. He makes too much money for them. It'll get hammered out eventually, IMO. Nate will fight when he wants to fight.