>> So I think you have an excellent thought there, and if you would forgive
me if I presume to offer a suggestion, it is good to ponder superheroes
that use their gifts to help the species . . . <<

I have a whole series on that topic.

>> . . . but why do they do it? <<

Different reasons, including but not limited to:
* Protect and serve.
* Money.
* It feels good to do what you do well.
* Vocation.
* A sense of duty.
* Feeling that nobody else can do what they do.
* Making up for past wrongs.
* Honoring someone's memory.
* Wanting to fix their little corner of the world. Or all of it.

>> There was a good episode of This American
Life on superheroes, and one segment included a fellow who had been
asking people to speculate on the subject in a personal way -- what
power would you want? and what would you do with it? -- and reported
that not one of them ever said they'd use it to fight crime. <<

Then it's incomplete: there are some people doing just that.

Most people with extraordinary gifts don't use them for fighting crime, though, or at least not directly. There are lost of other problems that need solving.