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?
That’s not their question though. Their question is about why build nukes when you can achieve the same effect with a shield and a lasgun.
You can just people do neither