I think back and I find it strange how Xbox was able to sell more than the GameCube. The first-part games seem a lot stronger on the GameCube than the Xbox, and the third-party support for the GameCube was far better than the Wii U's today. It seems that several third-party games on the Xbox were also released on the GameCube.
I hope I don't like sound I'm bashing the Xbox, because I really do think it was a great console. But what was the reason for gamers chosing the Xbox over the GameCube?