I can't remember if this is established in Frank's books or instead retconned by his son, that all AI and computerization was banned after the Butlerian Jihad.
My recollection - and I admit it's been a while - is that the events of the Jihad were expanded on in some of the Brian Herbert / Kevin J Anderson works, but that the basic notion (electronic computation forbidden, and why) was well established in the very first book.
"Thou shalt not make a machine in the likeness of a man's mind" is cited by Paul from the OC Bible in Dune.
There are countless passages in the original series where people recoil in horror at even the slightest thought of things like computers and artificial insemination.
Yes, I remember that, but don't remember if they explain why.
AI was banned, but I don't think computerization was. They had mentats to do what we'd use a neural network for today.
The jihad and it's repercussions in the form of outlawing all but the simplest computing devices is discussed in Dune.
It's established in the original books, not talked about much, but established. That's why there are Mentants.
That was in the movie. It's the whole point of the Mentats.