At the end of Avengers: Infinity War Thanos snapped his fingers and that erased half of the life in the universe etc. But to my understanding there is no rule book with the gauntlet. He snapped his fingers because that's how he decided to channel his intentions, he mentioned at one point that with all 6 stones he could simply snap his fingers and half would cease to exist (paraphrased badly).
So why did both the Hulk and Iron Man need to do the same in Avengers: Endgame?
Almost as if snapping fingers was the only way to achieve this particular task.