Gamecube arrived so late (especially in Europe) had no DVD, and PS2, starting in 2002, had the GTA games phenomena and GC not. Don't expect Metroid Prime can compete to that, even being a phenomenal game even today: Switch "remade" port (is basically a port) sold pretty well 20 years later, including in some markets where the original one sold practically nothing, because many did not even knew the game or even the GC existence. By that time many media was full on PS2.
Basically if Gamecube was launched a year before (I repeat, it was launched in May 2002 in Europe. By all accounts TOO late) with DVD reader, perhaps it would had a great option to success or at least, to have a great portion of the market.
GBA had no competiton at all, literally (Neo Geo Pocket Color was already dying).
Plus, Pokémon was a total deal for kids.
Plus, GBA was compatible with GB/GBC games from day 1.
Plus, GBA SP was very nice and portable for young adults.
That's why.
The first reason (the non-competition situation) is why Sony decided to launch the PSP in 2004-2005, thinking it would destroy Nintendo in the portable market. But... Nintendo DS appeared at the very same time, and we all know what happened :)
