Why would he sign and play? To hope he gets traded? Then the jets can easily do what Tampa did with drouin and just refuse to trade him. The only leverage Trouba has to force a trade is to holdout.
His options dramatically rise if he is signed.
The stances right now are the Jets want him to play for them, he doesn't want to play for the jets.
Okay next step, the Jets want to send him someplace, Trouba is unsigned so needs to sign wherever he gets sent. Jets have teams A-F in mind, Trouba has teams F-K in mind. Team F knows this and doesn't make a competitive offer so Jets decide to sit on his rights.
Everyone is unhappy with this scenario, Trouba decides to sign for a term he can live at, at a AAV that is worth his while, Jets are now free to trade him to teams A-F at a value they are happy with.