It's kind of an oxymoron of a statement ... Mario isn't cool to 14-19 old "boys" and 30 year old manchildren who live in their mom's basement ... but that is in an inherently "uncool" demographic to begin with. That's the dorkiest group of people you can get.
That said there's even a lot of 14-19 year old boys who like Mario just fine, even some manchildren will put away Destiny to play some Mario sometimes.
If you put Mario on iPhone, he would easily be one of the most downloaded apps by "normal" adults (as in people with a life). Nintendo's issue is that trying to sell proprietary hardware to get people Mario (who they like) is not easy in the age of smartphones/tablets.
I can like a friend just fine, but if he doesn't have a car that doesn't mean I'm going to drive 45 minutes out of my way to pick him up all the time. Sometimes I might, sometimes I won't, that doesn't mean I dislike him or he's uncool, it's just a pain in the ass to accomodate meeting up with him all the time.
Not everyone wants to buy a $300 seperate console they wouldn't buy otherwise just to play 1-2 Mario games and a lot of adults don't want a game handheld period, so that leaves the 3DS out. Mario isn't "uncool" ... but Nintendo hardware ... ehhhh. That might be where your "uncoolness" is coming from.
That said ... which franchise in the last eight years have sold more than the Mario platformers or Mario Kart? Call of Duty, ok, and what else? *crickets*. Not bad.
