That's just because it was the Omega version of WarioWare being shown then. Mini-games are still in the regular version of WarioWare.
It wasn't the Omega, there were all the platforms there like Project M. Unless for some reason it's the only Omega with platforms.
The only time I saw Warioware stage havee no minigames is when unlocking Wario.
Makes me wonder if there is another stage form. (Like no Hazards?)