Bear in mind that Kirby Air Ride came out in 2003, on a console that’s only meant to be hooked up to CRTs. How many users back then do you think would’ve had access to this feature in the first place? Or would still be playing this game if/when they upgrade later?
Gamecube doesn’t have enough RAM to preload everything at startup like that, you have to go through the menus and pick a game mode and map to load.
Surely if it needed that startup load anyway, then Sakurai wouldn’t be saying he turned the license down in order to get players in the game faster. I’m going to trust Sakurai’s word here!