Why is that bad, though? If you've read the book, then you've already experienced the story.
I can think of a couple of reasons, and I see where they're coming from on this. If the novel was good enough for them to make a movie out of, why just take the characters? They'd be more effective at creating an entirely new property at this point. If the end doesn't justify the means, then you have disappointed people who've wanted to see the novel's story on the big screen.
I actually think miniseries have worked better in translating novels, particularly long ones. Instead of only having an hour and a half to fit your story into, a miniseries can have more in-depth details and slower pacing when needed.
Ken Follett's Pillars of the Earth was actually a pretty faithful adaptation. Somewhat ironically, the adaptation of its sequel was not. It omitted large important chunks to the story and even changed the twist at the end to have it not make any logical sense.
There's also been a recent adaptation of Pillars into an adventure game/interactive novel that was fairly faithful as well.