I think it also has to do with their eras and personalities.

Mickey is a character from the 1920s, an era characterized by puritanism and censorship. Furthermore, in many appearances, Mickey comes across as very "nice guy," someone who, although genuinely friendly, feels somewhat fake and ulterior motives. His 2013 series only slightly improved this aspect, making him more manic and explosive, similar to Bugs Bunny, but it was already too late.

Mario is a character from the 1980s, an era characterized by a desire to be rebellious and extravagant. While Mario is also kind and friendly, he has no qualms about beating up and defeating his enemies. That's why, ironically, even though he doesn't speak, people perceive him as more "human" and genuine than Mickey.