I know this is a question that goes in cycles but I couldn't find anything on google and cba to think of different keywords for searching now, so I am rather gonna ask. I am not sure if this was ever clearly answered in manga/databook or in interview of Kishimoto, but I think I once read something where it was explained pretty well. Now I am not sure if it was just a well-thought theory or an actual official explanation, but I am sure I will get what I want here. So can I get the reasoning for the question in title? I feel like it's something obvious but I can't recall the detail right now.