Because their inclusion in the Super Mario series is debatable.
Mario Land 3 and Mario World 2 both primarily feature a different character that is not Mario, a gameplay style significantly different from regular Mario games and they both went on to inspire their own series of games that have little connection to Mario.
Mario Maker games and Mario Run are games that look like main Super Mario games but their main gameplay features are entirely different (building and auto-runner, respectively).
Luigi U and Bowser’s Fury weren’t originally released as their own game, as Luigi was Mario U DLC originally and Bowser was bundled with the Switch rerelease of 3D World.
The odd one out here is Super Mario Special, which doesn’t have the same problems as the other games and should probably be considered an official Super Mario game. However due to its low popularity, the fact that it wasn’t developed by Nintendo (only licensed) or released on their console, it’s filled in
Mario Land 3 and Mario World 2 both primarily feature a different character that is not Mario, a gameplay style significantly different from regular Mario games and they both went on to inspire their own series of games that have little connection to Mario.
Mario Maker games and Mario Run are games that look like main Super Mario games but their main gameplay features are entirely different (building and auto-runner, respectively).
Luigi U and Bowser’s Fury weren’t originally released as their own game, as Luigi was Mario U DLC originally and Bowser was bundled with the Switch rerelease of 3D World.
The odd one out here is Super Mario Special, which doesn’t have the same problems as the other games and should probably be considered an official Super Mario game. However due to its low popularity, the fact that it wasn’t developed by Nintendo (only licensed) or released on their console, it’s filled in