I don't think any really successful Mob boss feels too much guilt but I guess that could be a motive. I think the more likely motive is to, as you write, get good PR. Back in the day mob experts and law enforcement created analyses of Mafia families that had all these little boxes and arrows when the more appropriate analogy may have been the cosca (artichoke).

Whether fictional or real, a mob boss, captain or soldier who did favors for non-Mob people in the neighborhood was making connections that he might be able to use some day. It's a way of binding people to you very closely.

Maybe because a mafiosi did something nice for someone 1 day out of the year, someday down the road someone tells him of an unmarked FBI surveillance in the neighborhood, or he's able to reach out to a jury member whose brother-in-law he helped out of a jam or he gets early information about pending indictments or someone tells him about a criminal opportunity he doesn't know about or a cop looks the other way on his bookmaking deal because he protects the cop's elderly mother from neighborhood thugs or he gets a really good deal on his transmission repair or whatever.. Basically I think this would just be about building a network of people you can call on in a pinch as well as playing neighborhood big shot.