there is a cynical side to me that thinks a lot of them are used for cash laundering but that is based on no material facts whatsoever.
The thought had crossed my mind and material being the ironic word here, many high end shops, leather, suits and smart wear, sport shops perhaps always empty. Decathlon is an exception though its a sportsmans playground, what a shop i should think that has a kill off zone of around 15 km radius, similar to other big stores.
Doesnt help that the staff are rude as possible usually give you daggers the minute you walk in as your disrupting them from their daily Perogi eating routine, well thats one excuse. Ive tried on jackets in such shops with my Polish wife and all of a sudden in turns into a biatch fest between my wife and the shop clerk.