The Stretchers was a surprise release for the Switch last week, having been announced and launched all within 24 hours. Obviously the release wasn't a surprise to Nintendo, as they created the game! That said, it seems like Nintendo might have been waiting a decent amount of time to release the game.
Dataminer SimonTime went snooping around the backend of the Switch eShop, and found out that the game's first upload was all the way back on May 29th, 2019! Whether that upload was the finished game or just a dummy file is unclear, but it's surprising to see just how far back the game's first appearance on the eShop was!