Mario Game Mains

Can someone please explain why in Mario games, my Main is always changing.

Mario Kart Wii: Baby Luigi

Mario Kart 8: Bowser Jr.

Mario 3D World: Blue Toad

New Super Mario Bros. For the Wii: Luigi

Mario Party 8: Toad

Mario Party 9: Yoshi

Mario Party 10: Bowser Jr.

AM I OKAY?? And the thing is, I will change to a game, see the character I played 5 seconds ago and say "Imagine using them." With COMPLETE honesty and conviction.