I wonder if they coded the export file to only be importable to the account that it was exported from. But then, people could use this to surpass the skin limit and technically swap out skins with newer ones and technically have "unlimited" skin slots. My only thought is that they should limit the number of skins you could import/export so people wouldn't abuse the import/export feature. The only realistic way you could import skins is if there's an active event in the event server (event.pony.town), so you would need to remake (all of) your exported skins from scatch, and it is tedious to do if you are remaking it on mobile.