It's kind of sad that Doctor Sleep did so poorly at the BO... from what they say now, it might end up losing $30 million, if not more, after all the costs are figured out balanced by world-wide BO. It's a decent film, even if not the best, and deserved what positive review it got.
Meanwhile, the Pet Semetary remake earlier this year made more money, made a profit... and man, that film sucked. Wasn't awful (the acting was better than the original) and had a few creepy moments and tried a few big twists, but was also derivative and off the rails. Like, it was great at times because it was so bad in the ending and SHAMELESSLY so -- the directors knew it and simply did not care, so... I can admire that. But it certainly did not adhere to the spirit of the text, it felt more like a remake of the earlier film... so twice removed from the book. It is really a B movie.
Why did Doctor Sleep do poorly? Maybe released the same weekend as Midway with Veterans Day around wasn't great. It's after Halloween now, people are moving on to their Christmas jollies. Not sure how many people read Doctor Sleep (I'm reading it now), and while there's film viewers who appreciate The Shining, Stanley Kubrick did not direct this film regardless. it's almost like there's a bunch of niche categories that are reductive, not additive -- people might be less interested because of what the film is not (all the influences are partial, so they can feel watered down), rather than excited about a piece of what the film is that is of interest.
AS I noted, the film was decent but not at the tip-top of King films, and then ending felt kind of flat/subdued. I think Flannigan's "Gerald's Game" adaptation was stronger. But Doctor Sleep does have some great parts. I do like how King's world is interconnected, and they even made this tighter in the film -- for example, they referred to the one girl as a "pusher" (which folks who are familiar with "Firestarter" will recall regarding Andy McGee's psychic power).
AS noted elsewhere, IT Chapter 2 and another film still made a killing, so the losses can be easily absorbed. It's just disappointing if this would dissuade future efforts to adapt King's works from being made.