They have busted him before, privately. His account was closed in 2020 (when he was 16) for cheating. They let him continue playing due to his young age. According to Chess.com, they were going to ban him before Magnus even tweeted anything about the incident. They have intentionally held evidence private so as to respect the privacy of players throughout the ordeal. The only reason evidence was made public was due to Magnus' public accusations (which you could argue were emotionally motivated, yes).

For the same reason, it would be humiliating for tournament organizers to pause the tournament to do a full shoe and cavity search in the moment. It's also ridiculous to expect Magnus to run to tournament organizers and make such a request. I have a feeling even if he did so it would only lead to more people calling him a "man baby."