At this point it’s a fairly well-known fact that the American Super Mario Bros. 2 isn’t an original game, but instead a conversion of Yume Kōjō: Doki Doki Panic, a title that was being developed in-house by Nintendo at the time. The original Japanese Super Mario Bros.
2 is a direct sequel to the first and is generally considered much harder and less forgiving than its predecessor. If Americans had gotten the original sequel, it was assumed they probably would have lost respect for the series
. Read more on screenrant.com