I guess Nintendo's in a banning mood today! First up, they removed a Super Mario Maker 2 level by master course creator GrandPooBear, and now they've yanked a stage named "Storm Area 51." The stage was removed due to “inappropriate or harmful content.”
With this stage's removal, I can at least see the reasoning. For those who don't know, the "Storm Area 51" movement is aiming to get people to actually storm the real-life Area 51 on Sept. 20th, 2019 to see what the government is hiding. This has actually lead to the U.S. Air Force warning people not to enter the area, as it's illegal to do so, and the area is used for military training. Nintendo simply doesn't want anyone taking the advice of random people, which could get them into trouble at Area 51.