The purpose of the game is to kill random, innocent people; most of whom have done nothing to you and are unarmed. The game rewards you for killing people in this fashion.
The purpose of GTA 5 is not to kill innocent people. You CAN, if you SO CHOOSE TO, but it is not the purpose of the game. There is no special reward for murdering innocent people in GTA 5 (other than they drop some cash, but that is considered an act of theft, not a reward). In fact, you will draw the attention of the police who will try to hunt you down to bring you to justice. (aka consequences and punishment for committing murder - not rewards.)
In fact, based on your reply, people could argue that you can cause Mario to commit suicide in Super Mario Brothers by intentionally letting him get eaten/burned by Bowser. Suicide is an adult topic.
Does Super Mario Brothers have a Teen or higher ESRB rating? No. It's rated E for Everyone. Why? Because the purpose of Super Mario Brothers is not to commit suicide. It's to save the princess, who is likely in another castle.