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?
Well in addition to the other answers, out of universe, the answer is power of plot. Simply nuking the shit out of everything wouldn’t really make for an interesting story.
Right? Magic is real in Dune, we don’t don’t need a hard sci fi reason for every missing technology frank Herbert didn’t think of in 1965.
Nukes play a rather pivotal role in Herbert’s book though. He definitely thought of them.
I am talking about OP’s idea of using lasers instead Nukes, nukes are fine, they fit the theme of 50s/60s geopolitical allegories rather perfectly. Using hard sci fi logic on a space opera sounds like an exercise in insanity, but OP is free to drive themself mad however they like. It’s Lemmy, we’re all mad in one way or another.