Well, it depends on what you mean by 'backstory.' All the heroes have backstory, not all of them have these little fiction bits.
This fiction is stuff I wrote in my spare time for my coworkers. I have to write backstories for all the heroes, so I can write their dialog and cast them, but that stuff tends to be dry and, as a result, busy people don't read them.
So to sort of entice more people to read more about our heroes, I wrote these. And now we're sharing them with you beautiful people!