[Lestrade]

Harry Potter was initially aimed at kids, so the shorter length made sense. The books sort of got longer and darker as the target audience did, and honestly by the time the fourth one came out Rowling could've written basically anything she wanted because she was raking in the dough ^_^*

I will say, as a fantasy writer, that worldbuilding in a short span of pages can be REALLY REALLY HARD. When I turned my NaNo into a short story the single hardest aspect of doing that was figuring out how much of the backstory of the world and the races to leave in and how to go about getting that information across without just infodumping.