I have been reading that the deal basically includes almost everything Iran has been asking for. Perhaps, the folks around Trump understanding the cliff we are racing for are keeping Trump out of the loop and hope he will just sign something because the pain that is coming has the potential to force a ground war America is not prepared for.
Once Iran closed the Strait, Trump's surrender became inevitable. The rest has been a combination of him slowly coming to terms with the inevitability of that outcome, and buying time to come up with a way to spin the catastrophe as a success.