If a team truly believes a QB is not the QBOTF which is the opinion you hold when it comes to Tua why wouldn't they get what they can for him trade wise and move on. You say the organization saw what you saw which means they saw that he was a bust which means his stock is not going to get any better. Tua had a better rookie year than Rosen and Rosen fetched a 2nd, I have to assume Tua would have gotten at least a 3rd.
If Tua doesn't take the next step this coming season his value will drop even more just like Rosens value dropped after his 2nd season. It doesn't make sense to not trade him now unless unlike you they believe he WILL improve this season OR they aren't ready to move on from him and wish to further evaluate which means they weren't trying to move on from him.