If the Dolphins trade Tunsil to Houston knowing that they can't re-sign Clowney until the off-season they are morons. IMO that's the biggest hold-up in this situation, the difference in Clowney's actual value as a football player, and what is he worth to another team to acquire when you factor in the massive risk involved in that he can walk and you end up with nothing. If he could be re-signed to a multi-year extension immediately, ergo, teams would be given permission to talk to his agent and work everything out in advance, you'd be correct, but this isn't that situation.
Zay Jones isn't ample compensation, not even close. But to Houston, if Clowney is really going to sit he adds no value to your football team and they have immediate needs at multiple positions. The longer he sits out the fewer games his acquiring team will be guaranteed to have him on the field which depresses his value even more. After the trade deadline he has no value at all to Houston apart from the 3rd round comp pick they MIGHT get (again, assuming he truly is going to pull a Leveon Bell maneuver).