A lot of people on this forum expected Super Mario Maker 2 to be a great home run success and a lot expected the title to easily pass the 10 million mark. This isn't the case. The game has not reached the 6 millions copies sold and is showing zero leg.
The port of New Super Mario Bros U is at 8.3 millions and is going to pass 10 millions ultimately, this is the game that people who want 2D Mario are picking right now. Super Mario Maker 2 is turning potential Mario gamers away and people are buying a 8 years old game rather than the game released last year.
Most people want nothing to do with a level editor and most people would rather play levels made by professional level designers than search among thousands of amateur designed levels.
I think the Switch is such a success that Nintendo could launch a real proper 2D Mario and turn it into a 20 millions+ seller like the Wii version was.