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?
The reaction between a shield and laser is completely random, not knowing wether you are going to vaporise a few molecules, an entire city or everything in between makes it very unreliable for warfare purposes.
And you’d probably find the whole Landsraad against you, as using atomics is outlawed. While a bomb like that isn’t an atomic weapon by definition, the effects are the same and it stands to reason that they’ll therefore still retaliate in full force.
The whole lasgun-shield interaction concept is one of the hand-wavy parts of Dune, kind of like the eagles in LOTR, or the ridiculously inaccurate laser blasters in Star Wars.
Shields in Dune are common defensive technology, which means that lasguns would almost certainly have to be outlawed altogether to prevent some random encounter from turning into nuclear apocalypse.
In the first movie, I think Villeneuve deals with it somewhat haphazardly. The use of a lasgun at the agricultural research station perhaps makes some sense because shields can’t be used in the open desert without attracting worms. On the other hand, they show lasers being used at the first Battle of Arrakeen in close proximity to other ships that are shown to have active shields.