Tbh the GameCube failed because it had zero direction of what it set out to do. It was a pathetic attempt to compete with the PS2 with its lack of 3rd party support, colorful and toyish like design, and lack of DVD or online.
It also had nothing that made it really stand out, Nintendo consoles can be successful if they offer a thing that'll make them stand out from their competitors, we saw it with the DS,Wii,Switch ect... but GameCube had very little going for it. Maybe the only thing that was remotely cool was the GBA/GC add on but it required 2 separate consoles and wasn't enough to stand out. Every successful Nintendo console needs that huge hook to get people on board, otherwise it just looks like a sad attempt to be a PS2 clone box, which was exactly how the GC was perceived. Nintendo tried to make it clear in their marketing that the GameCube wouldn't focus so much on their competitors and would just focus on trying to stand out, but the GameCube was anything but a console that stood out.
But its crazy how bad Nintendo's image was with the GameCube to the point where NOA employees considered changing the iconic Nintendo logo into a graffiti design just to prove that Nintendo was edgy and mature.