Between Nintendo's significant consoles. The Gamecube and the Wii U have their cult-like fanbases who think these consoles are like the Messiah, but they weren't major Nintendo consoles; it doesn't seem Nintendo ever saw them as such, either. While N64, Wii, and Switch marketing were all prominent, all over the place, the Gamecube and Wii U were rather mute; in addition, Nintendo didn't release any major flagship titles/killer apps for Gamecube or Wii U.
Most importantly, Gamecube and Wii U never had a major interface upgrade - they were more or less, "hmmm, we need to have some kind of upgraded hardware to fit the timeslot, but we don't yet have our next big thing concept ready" - which is really the main reason why they are more like stopgaps.
Perhaps they were not marketed well in Germany but they were as heavily pushed in the US and Japan as any other Nintendo console.
And no flagship/killer apps? Are you forgetting Smash Melee? Metroid Prime? Wind Waker? Mario Kart 8? Splatoon?
Besides, the definition of a stopgap is a temporary device with a planned replacement already being developed.
Massimus - "Trump already has democrat support."