Sorry, but "why" is not an aggressive word. Asking somebody why they did something is no more aggressive than asking what their intent was.
If "why" is coming across as aggressive in a code review, then it's because your overall code review experience is too adversarial, and needs to be reoriented to be more about achieving quality code, and less about blaming people for mistakes.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.