And yet Maximum Velocity on GBA sold almost as well as F-Zero X did (1.05 mil and 1.1 mil respectively, as of Dec 2014). Also, in regards to you "GameCube sales were poor, so low sales on GameCube isn't a surprised", Star Fox Assault ALSO sold low on GameCube - in fact, it sold worse than F-Zero's debated 1.5 mil (Assault sold ~900k total across all regions, while Adventures sold ~1.82 mil). And yet THAT game got a follow-up a year later on the DS and, despite Command's failure, two more games after that, meaning it lasted longer than F-Zero before being shelved (same with Metroid, funny enough, since Prime 2 sales were below half the first title's). And even if we took your "I didn't have fun playing them" opinion as an argument to discard the GBA/SNES titles, that STILL wouldn't have ruled out a Wii follow-up to GX if it was as successful as claimed.
So I ask again: why wasn't F-Zero GX's "greatness" enough to save the F-Zero series from abandonment after the absolute financial failure that was F-Zero: GP Legends/Climax? Why did GX not prevent those games from being the straw the broke the series' back?