How come Harry didn't even try to help this guy?

Maybe because 5 minutes before that scene happened, the dude was pointing a fucking gun at him.

Because it's Kaufmann getting exactly what he deserves. He constantly threatened Lisa with drug withdrawal, taking away her supply and harassed her to look after Alessa in hospital basement. Not to mention he played a mistrustful hand in allowing the events of the game to take place.

Kaufmann was never alive to begin with, like Lisa he was just another specter created by the town and played out a part in what Harry saw during his ordeal.