If you’re importing a library into Plex that’s already organized in a hierarchy of subfolders, leaving it that way is much easier. With a bunch of short clips/unlabeled videos only organized by folder, I don’t want to take the time to put them into collections when they’re already organized as is.
(On a related note, I do understand that folder view is less used than the default view, but displaying thumbnails in folder view like is done on desktop would be a great improvement as requested here: [Request] Posters for Folder-View)