Apparently in Japan, their Apple Stores just display all their devices without any security tags on them since it’s built within a trust system where an individual is expected to not shoplift (due to shaming culture) as public face and reputation matters to them along with heaps of CCTV and stricter laws. However, try doing the same thing in New York or Seattle and see what happens…
It’s because demo units are registered per store.
On top of this, if I remember correctly iPhones 15 and newer have special versions of firmware which do not let you enter DFU mode to remove the demo mode.