Smotritch knows there is no such thing as work out the details later. If they dont work out the details in advance as part of the agreement, he will no longer have any power to demand authority over various realms he wants to be able to to influence and then he will just be a puppet Minister with no real sway on government decisions. So then he can leave the government! Well, not really. He should plan in advance to be the person who breaks up the full right wing government? Netanyahu will destroy him over that in the next elections that would happen as a result. 

It is far more responsible and reliable to work out the details now and come to an agreement and then form the government. Let's see if Smotritch can withstand the pressure. And let's not forget, while publicly it seems to be Smotritch holding things up, no agreement has been arrived at yet with either UTJ or Ben Gvir. Shas is the only party Netanyahu is willing to give pretty much everything they demand - to the demise and frustration of all the other parties.