I think the initial appeal of the comics was that they were going to tell new stories penned by King. Once King became less involved, then their canonicity was in doubt.

As for the more recent arcs that are retellings of the original novels, I can see the appeal for those who haven't read the books, but sustaining that appeal over a dozen story arcs is tough. I have most of the comics in the hard cover collections, but I admit I haven't read the later ones.