Predicted rainfall kept being revised upward as more data became available - up to 20". By shortly after midnight both AccuWeather and the National Weather Service predicted massive flash flooding and urged evacuation. (Incidentally - very similar to the 1987 flood which also killed several campers.)
The catch seems to be getting that evacuation message to the camp.
There appears to be no cell service (and while campers were prohibited from phones/internet, staff had them). Cell phones capable of receiving an emergency broadcast are no good if there is no cell phone service.
It isn't clear that an emergency weather broadcast was made - even if cell phones have service, if no message is sent they won't receive it.
What backup plans did area make after an eerily similar flood in 1987 (and several earlier ones). The area is filled with summer camps - did anyone bother to set up a plan to call these camps in the event flash floods were predicted? I have vivid memories of a similar "100-year" flood in the '60s. We weren't in a heavily populated area - but we used the information from that flood to plan for the depth of the basement in the house we built a few years later to ensure it would stay dry in. When the weather gods give you a trial run, you'd best not ignore it.