Superpowers, from a literary standpoint, can get a bit derivative and boring. It's hard to feel the stakes of a certain threat when the protagonist of a story can just superpower their way out of it.

The Punisher flips the superhero trope by portraying what a true to life superhero would probably look like. He isn't noble. He isn't invincible. He has no enhanced abilities beyond his ability to leverage violence and a pathological determination to pursue his own twisted vision of justice. He is a walking result of severe emotional trauma, and his coping mechanism is inflicting pain and death on others.

As a superhero archetype, he's very bleak. That's what makes him relatable to a lot of people.