It's the fact that there are no thumbnails for the files once the files are in the designated folder on the hard drive.
Seeing thumbnails is a personal preference for me as I would go to a folder, look at the files that were in it and then choose what I want to import into Lightroom.
Why don't you import all your images into Lr to start with and then remove the ones that you don't want in Lr. You can remove images from Lr without deleting them from your hard drive.



