Honestly? Because he’s a good character. No one takes his morality to heart that wasn’t already deeply damaged, but a character who builds their psyche and motivations around trauma and idiosyncrasies creates a fascinating piece of a story, nonetheless. Similarly, Breaking Bad is never viewed as a tutorial on losing your morality by a thousand cuts, people view it as the chronicle of an intelligent character intentionally blinding themselves to the damage they cause and reacting in a relatable way. The fall from grace and subsequent dwelling in hell is a beautiful story arc and there’s a reason it’s employed so frequently.