Today Kotaku brought it to our attention that Nintendo is deleting players stages for a variety of reasons, including being unpopular.
When Mario Maker first came out, Nintendo warned it could delete stages for a variety of reason. What the reasons are still are unclear, but Nintendo made good on their threat. Obviously stage creators are very upset about this.
Nintendo Originally Outlined
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.
What classifies a stage as being unpopular is not clearly defined. Why it really matters goes unexplained as well. Maybe the Mushroom Kingdom Cloud only holds limited data. regardless the reason, I felt Mario Maker stage creators might want a heads up on this news. Time to step those stages up!