[narism]

I believe this is because of the widespread use of shield projectors which repel anything moving too fast (faster than a slow knife stroke or hunter seeker). Some other interactions around shields:

Lasers hitting shields basically results in a fusion explosion which would bring down the wrath of the Houses/Imperium.

Shields are not used much on Dune due to shorting out from storms and attracting worms. This results in some use of projectile weapons when the Harkonnens seal the Atreides troops in caves with mortars or the Fremen shoot the noses of off the Emperors spaceships with artillery.