GBA was still riding the initial Pokemon craze which started in the West in 1999, so 2001 was not far off from that.
GameCube just had way stiffer competition and much less margin for error, the PS2 was the PS2, and the XBox had Halo. GameCube honestly was a much better system than the GBA, it just had far stronger headwinds going against it.
In hindsight the GameCube probably needed to launch in fall of 2000 and/or they needed to form a partnership with Microsoft and talk them out of making their own console and supporting them instead against Sony (which really would have been more to MS' benefit anyway as XBox hasn't been successful in supplanting the Playstation, lots of wasted money for not a lot of return).







