Maybe they are; and are sworn to secrecy 
…
Re Quidditch in general: I’ve always had the feeling that Rowling is a non-sports-fan, in fact a disliker of sports – and has had fun inventing, in Quidditch, a completely insane, wildly complicated, and overall impractical sport; which nonetheless has large numbers of fanatical devotees, and “learned scholars” about its intricacies.