In the Dune universe, when a laser weapons hits a shield, both are destroyed in a nuclear explosion reaction.
So instead of building nuclear weapons, wouldn’t it be easier to tie a timer and a “parachute” to a laser gun and drop it from orbit onto your enemy’s city?
I’m not sure I’m giving them far too much credit when you’ve sort of already proven my point by bringing up the multiple times it has been ordered and yet still avoided. I’m sure the situation would have changed if the person’s responsible for launch believed themselves and their families to be dead already, but a chance at anything else is better than nuclear MAD. There’s a hell of a lot of reason not to press that button.