GC was cheaper and it had more residual Nintendo fans from their glory days. Basically that number of hardcore Nintendo fan of the 80s who buy new Nintendo systems is lessening every gen. Wii had the casuals so it's hard to tell, but now we see again the decline in fans of their franchises who are willing to invest in new stuff. Their holdover is pretty good but they can't generate new fans for whatever reason. There are exceptions to be sure such as my neighbors who have two small children who have a WiiU and never owned a system themselves but these are rare and the larger movement is less and less newbies each gen excluding Wii. NES 60, SNES 40, N64 32, NGC 21, WiiU 18 hopefully?

The name and marketing. GameCube also had earlier key titles like Zelda and Smash. Along with high-profile third party games like Soul Calibur II and Resi 4 (which was a timed exclusive).

Because Bayonetta 2 has massive frame drop issues.

It is? How much did the Gamecube sell last week, didn't think it would be higher than the Wii U.

i selected other, i think it has to do with two things one is the god aweful name, alot of people here me say WiiU and think Wii and dont know the difference, the other factor is alot of gamers see the gamepad as a gimmick and dont know or dont care that you can use the pro controller for nearly all the games.  after motion controls pushed me from the Wii games i was hesitant to get a wiiU with that gamepad.  

One big aspect was that the name helped people see that the Gamecube wasn't just an expansion of the N64, yet lots of people were confused about the differences between the Wii and Wii U, along with the price.

The Gamecube had better games (for its time).

Wii U is waaaaayyyy too expensive, and its marketing is horrible compared to the GameCube. I'm surprised it's even selling as much as it is.

Because the 6th gen was really just a 2 horse race, Dreamcast was the epic fail, and Xbox was a brand new player on the market.

Now coming off the 7th generation Xbox is an established brand with a decent core of fans, and Playstation seems to have won back pretty much all the good will it lost early in the 7th gen. Despite the lack of a 4th player in the market, this puts Wii U at a considerable disadvantage compared to GC.

At one point the GCN was selling for $99 while still in production.