I think it was equal parts wishful thinking, some units did negotiate for surrender and there were hopes it would mushroom, and part psy ops.
Psy ops is a useful tool and even if just a few hundred decide to surrender - it will save lives.
I seem to recall that Saddam extended his generosity to all of his generals by hosting all the the generals' families to stay at Saddam's place, free of charge, until the battles are over. They just might be too afraid for their loved ones to surrender. JMHO
Nam Vet