GCN only had "strong" third party support in comparison to the Wii U and late-stage Wii. GCN missed out on several huge hits and a bunch of various other titles. Western support dropped off a cliff from N64, with GTA and most FPS titles skipping the system, and while Japanese support was better, it wasn't nearly enough of a recovery to compensate and the Japanese audience further contracted. Throw in the lack of multimedia features that made PlayStation a household brand and the Xbox excelled at, no online features in a gen where Battlefront and Halo were making huge waves, and the "kiddie" design and reputation and it's not particularly shocking.
Xbox had much better third party support than the GC, and the biggest console multiplayer game in the world at that time (Halo) with the best online connection, and still only sold a little better than the GC.
I genuinely believe the GC deserved better for the games it had.
Pikmin
Luigi's Mansion
Metroid Prime
Super Smash Bros Melee
Super Monkey Ball
Star Wars
Eternal Darkness
Resident Evil
the system really had a fantastic library of games
if only word of mouth was as strong as it is today with social media..
the PS2 crushed the competition that gen and other systems never had a chance. there was unbelievable number of games releasing on that system, it was crazy...
I remember IGN even doing something like... game of the month, due to the huge number of releases..
and the marketing was dishonest for it with a lot of talks about how it is more powerful than a Super Computer
and even crazy things like this:
https://www.eurogamer.net/articles/article_29913
an integrated bundle of 12-15 PlayStations could provide enough computer power to control an Iraqi unmanned aerial vehicle, or UAV
and how this or that game use only 70% of the processing power...
hahaha...
haha..
how did i believe that crap at the time... ~___~