How they never made an online F-Zero for the Wii I do not know, but hopefully they won't add some terrible new mechanic to F-Zero Wii U or anything since F-Zero GX is basically already perfect.
-- Not changing this sig until I decide to change this sig. Started: July 6, 2005
Supposedly they didn't think an F-Zero on the Wii would be a big enough improvement over GX, in terms of the "wow" factor. With the Wii U they have HD though.