I'm surprised they don't mention the Dune prequel titled "The Butlerian Jihad," written by Frank Herbert's son according to the former's notes:
(with justification, imo - the crudity and stupidity of the "Extended" Dune universe books warrants this level of snark)
The butlerian jihad trilogy was awful though, it was there to give some necessary background information for the end of the series but when you've got characters with ancestral memories and characters that can see through time that probably could have been done in a much better way.
A more likely reason is that most of them are really badly written. The books feel as though the writers wanted to make a quick cash grab using existing IP, but completely misunderstood what the exact appeal of the original works was.
See also the reboots of Star Trek, Star Wars, Dr Who...