I don’t think dark rides are as popular as coasters, by any means. I think they are well-liked, but in this day and age, I do think that they are harder to market unless they have some kind of IP association, which is what gives off the impression that they are less popular.
In terms of other UK parks, DBGT failed to raise guest figures and doesn’t really seem to have resonated with the public hugely, and Sub-Terra wasn’t particularly successful either. Even Valhalla, which is (or at least was) critically acclaimed, is said to have not been as successful as hoped.