>>721068554
This isn't quite the slam dunk argument you think it is.
Mario is opening theme parks and enjoying that level of success because he is like Mickey Mouse: a sterile, unflinching cartoon mascot that is safe and can be stamped onto pretty much any product you choose. He is rounded, cuddly, and inoffensive. He is designed to be as broad and marketable as possible, which is fine, but doesn't leave much else to him. There is no personality there beyond 'OKEY DOKEY, WAHOO!' His own brother is the more interesting character. Plus the setting is the most generic candy-coloured thing imaginable. There is no real danger, no mystery.
Meanwhile, Sonic's universe has a bit more grit and edge to it. People die, permanently. There is lore. Cool music. I'm not going to act like it's the bloody Iliad, but there is actual stuff to latch onto. It damages the potential for broad appeal, but it's undeniably a more interesting universe than Mario's.