According to Herbert's lore, this was done out of fear of artificial intelligence. The House Atreides Mentat — as he was envisioned in Denis Villeneuve's 2021 film "Dune: Part One" — was a man ...
In Dune lore, Hawat is a Mentat, a human-computer who is loyal to House Atreides. David Dastmalchian played the Harkonnen's Mentat, Piter De Vries in the 2021 film but the character was killed off.