I think the Enid Blyton influence is direct - a bit jokey and a bit nostalgic, and possibly even a traditional marker of children’s literature that JKR was paying homage to. JKR mentioned the Malory Towers books quite recently in an interview. I agree that bad writing is a strong contender too, though!

I understand what's being said about film and agree that it would be 'inattentive writers' who responded to film in the way being discussed - inattentive to film as much as to writing because film scenes are painstaking creations and dependent on nuance and detail. I'm sure there are writers happy to leave the task of description to their readers' vague recollections of some similar sort of scene they've seen on telly. Afer all a whole book could be written in just one word: whatever ;)