In case someone is wondering. Charizard already had a smash amiibo long before the others, because Smash Bros 4 (3DS/Wii U) replaced the pokémon trainer, who had the three of them in the previous game, with only Charizard. Part of the compromises they made for 3DS was removing characters with multiple forms. Since Smash amiibo were created for Smash 4 originally, it had a Charizard amiibo.

In Smash Ultimate, “everyone is here” so they released the other two.