This seems the most likely reason. It is sort of like they teach in first aid. You don’t say someone call 911 because everyone thinks someone else will. You need to tell one person directly.
The problem here is that it is not a group of untrained bystanders stumbling upon a surprise emergency. There is supposed to be a pre-established chain of command and group to take these reports and ensure that they are investigated.
Hell, I was part of events where governors made appearances, and the county had their communication command post setup and even gave radios and a briefing to our volunteers at gates and all of the area leads to report anything directly to the command post.