*Points at Captain Toad Treasure Tracker once again*A listers are mostly protagonists, and characters that have extremely successful games. Toad doesn't fit these categories at all
This game was critically acclaimed and was deemed worth getting ported twice to Nintendo's current consoles and given two sets of DLC even five years after it's initial release.
I know vgchartz isn't the most accurate sales info but according to it's last update between the Wii U and Switch versions the game has two million, five hundred and thirty thousand physical copies sold.
Still waiting on the figures for DLC sales, 3DS(which was the worse selling of the three versions) and virtual copy sales but that Captain Toad has easily breeched that lauded million copy selling milestone with only Toad and Toadette's adorable faces pushing the product makes me think you're selling their appeal a little short.