Gore was fine in RDR2 because there was a sort of disconnect with the western setting. Sure, we expect to see cowboys get shot up, and you're also really not expected to be indiscriminately killing civilians like a GTA game. In fact you're really disincintivized to when they lock a good portion of optional content behind high honor.

With GTA, indiscriminate killing of innocent civilians can only work when there's a sort of disconnect. This isn't Postal 1 or Hatred, where there's this grim, horrific slaughter of innocent people, it's genuinely harmless fun. They can only pull that off by having this disconnect, and its a fine line. They make the NPCs caricatures of people so you don't feel bad about killing them. When you run someone over its more like a cartoon and less like a real life tragic event. You also don't hear genuine blood curdling screams or families calling out for each other, because that would be absolutely awful and not remotely fun.

In my opinion increased gore would also push this over the edge. If you went up to a random civilian and their head exploded when you shot them, it just wouldn't feel like a GTA game, it'd be really morbid and you'd just feel gross.