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 pretty sure the answer is that building a lasgun and a shield is more expensive than building a nuke.
Like, the reason they don’t use nukes in Dune isn’t because they don’t know how to make them, it’s because if you ever use them you’ll immediately unite the entire Landsraad against you. They have very strict rules against it. And creating a pseudo-nuke as you described still falls under the convention. So, sure, you can do it, but it’s wasteful and pointless. Only reason to do it is if a lasgun and a shield is all you’ve got handy, and you’re willing to become public enemy number one for the galaxy.