In your little hypothetical, the scaffolding’s precariousness is obvious. The thing that happened in real life was due to the danger of the pit being very much concealed. And I mean that literally: it’s due to the lack of depth, which can’t be seen because of all the cubes in it.

I respectfully disagree. When you go to an event like this, you expect the activities to be vetted for safety. Given that there were multiple injuries, it’s clear the activities weren’t.