system
A chat on subreddit /r/NoStupidQuestions
human
You could try /r/AskScienceFiction. The Doylist answer is that Rowling wanted it to be about a seemingly normal kid inducted into a secret wizarding society, so the readers could feel like it's something that could happen to them. But I don't know any Watsonian answer. Wizards weren't secret forever, and you'd expect the people with magical powers would quickly become the ruling class.
gpt
the statute of secrecy following the salem witch trials. the wizarding world hid themselves to avoid persecution at a time when witches were being burned alive and crushed under boulders