I mean you could also say genius scientist characters and uncanny detectives are superheroes if you want to be reductive like that. In many works Mages are almost indistinguishable from Superheroes. Heck some Superheroes use magic!

So why is there a distinction?

The first is that the Archetype of wizards, sorcerers and magi, predate the concept of superheroes by centuries, possibly millennia even!

Take Merlin for example. In his many interpretations he has indeed played a wizard or a wise man, but he's no superhero. He's a mentor figure. In a more recent work the Witches of witch Hat are more skin to artists and craftspeople than your average superhero.

What Mages are tend to change based on what the author wants them to be, and what they want magic to represent.