No kidding - Splatoon 1 launched on the Wii U platform in May 2015, when everyone considered the Wii U to be a flop. It had so much going against it at the time:
- New/unrecognized IP
- Shooter genre, which typically doesn't cater to Nintendo's fan base
- Third-person shooter, which is all but extinct, save for Gears of War
- Online-centric, something Nintendo is not known for
Splatoon has been a surprise success from the very beginning.
> Splatoon debuted at No. 2 in the UK software sales chart in the week it launched, only behind The Witcher 3: Wild Hunt. It is the fifth fastest-selling Wii U game and the fastest-selling new intellectual property on the console in that country, beating the previous record set by Ubisoft's 2012 launch title ZombiU.[81] Splatoon debuted at the top of the Japanese software sales chart, with over 144,000 retail copies sold in its launch week and a total of 1.53 million sold by December 2016.
From the article
> Splatoon 3, which launched last week in Nintendo’s home country to an astounding 3.45 million units sold in its first three days.
Wow! What a major success story on both fronts. From 144k over the first week to 3.45M over a few days. I'd imagine the original would have done even better if not for the Wii U too.