Thousands, maybe millions of Mario Maker levels have been made, that is a lot but can Nintendo really store that many? No, no they can not and Nintendo has made it clear that any low popular/inactive levels will be deleted:
Low popularity isn't made very clear, but apparently this is happening:
Have any of your levels been deleted?
Notice regarding course uploads
Please be aware that after a fixed period of time, courses with low popularity will be automatically deleted from the server.
Nintendo reserves the right to use uploaded courses and related data, either as-is or with alterations, for either commercial or noncommercial purposes without compensation to the uploader.
Low popularity isn't made very clear, but apparently this is happening:
Apparently, Nintendo is in the habit of deleting levels from the network permanently with the level marked in the player’s save file with a ban from the network so that that it can never be uploaded again, even after it’s edited to reduce difficulty or alter it completely. Now, I know this got some attention with players uploading levels exploiting glitches, but many of these deleted levels don’t exploit glitches but rather haven’t accrued any stars and have zero percent completion rates (either due to difficulty, little traffic on the level or both).
Have any of your levels been deleted?