The lore for most of the characters is that Wario realized that Mario was making a ton of money by making games, so he hired employees to make games for him. That's what the WarioWare games are.
Problem is that Wario's trying to make WarioLand 5 but he doesn't know how to make games, so he hired random people who just do random bull** in the hopes that whatever happens results in Warioland 5
So he's got a witch, a pair of aging disco bros who hate each other, an exercise guru, a mad science student, and Dr. Eggman's illegal immigrant knockoff. Among other things.
