Someone made an angsty theory on the super mario bros movie tv tropes. That instead or their dad tbinkie hes bringing luigi down,that perhaps in some way he coddles luigi?

I dunno... Mario's Dad doesn't strike me as a coddler. If he coddled Luigi he wouldn't have been so blasé about Uncle Tony pulling food out of his hands during dinner, and wouldn't have had such an overwhelmingly positive reaction to Luigi helping Mario fist fight a giant fire breathing turtle monster.

Now, there is a chance he's softer on Luigi compared to Mario, but Mario's clearly the one leading the charge in their shaky business endeavors.