Chinese airline executives punished amid photo outrage
https://edition.cnn.com/travel/article/china-air-guilin-safety-disciplinary-action-intl-hnk-scli/index.html
What I wanted to refer to is written at the last part of the article.
So, The reason why ordinary passengers must be away from cockpit is deadly accident which happened due to operation by a child.
Anyway, it was fortunate that this incident didn't cause any fatal accident.