The main reason I see for gamecube's failure was bad management from Nintendo.
From marketing it as a kids thing (which ruled out a lot of older gamers) to missing opportunities the other two big consoles used like being able to go online. Even if it was rudimentary on the ps2 it still worked. With Xlink you can play many games to this day. Try that on the Gamecube. There are ONLY 4 online games and 4 lan games. They work, but try to get enough accessories for all consoles together. The modem/network adapter itself was and still is expensive (not mentioning the low supply from the start).
They kinda learned from that mistake, slammed together 3 dvd boxes and called it a day with the wii.
And I need to agree with one of the posters on the forum. The Wii U sold half of the amount the gamecube sold. Who even remembers the Wii U? I'm 100% sure parents around the world went into stores to get this Wii thing and bought the old one, because it was cheaper and had Wii in it. It was expensive, useless tablet kinda thing you always needed to use - even when the game didn't needed it. And even forced it upon the player - see the StarFox game. Do I look like a garden bamboo
filling with water and changing sides all the time?
Oh, yeah. So far the only game, which I think used the pad really well, was Project Zero V / Fatal Frame V. Being able to use the pad as your camera was awesome and bought a lot more movement into it.