And it wasn't a particularly impressive game. There's no shortage of endless runners on mobile, and Nintendo didn't do much to differentiate themselves, so it's no surprise nobody bought it.
As for the game itself: I've played it, and it's a pretty decent runner with the physics of New Super Mario Bros. Wii/U, but it's just not the same as the more full-fledged games. It's fun to pick up and play, but not groundbreaking or particularly special.
It seemed like an anti-piracy move because the game didn’t naturally need to be online. But I never thought iPhone app piracy was much of a concern.