Much of the search in fact it might have been most of it wasn't even in the area of the bridge. People were searching far away from that area, in town, etc., etc., etc.
The limited and rather ad hoc search was for two missing girls, I've yet to come away with the impression that anyone thought they were in any danger. Which makes sense to me, considering the small area in question where they went missing, and more so the fact that people weren't thinking the worst in Delphi, IN, on Feb. 13th, 2017.
They probably figured the gorge area had been searched enough, already, by 10PM or so when people had already started heading home. Most of the gorge search focused on the area around the bridge and west of there. In and along a shallow creek.
I guess I don't understand what the big deal is about the search, people were probably within mere feet of the girls that evening but didn't see them. I'm guessing within 200 feet or maybe much closer. So effort was made but in the darkness it was difficult to see any great distance along much of that gorge area. It's happened before with searches and it will happen again.
Last but not least the safety factor of having searchers of all different ages and a range of physical abilities, searching in pitch darkness along a gorge with heavy vegetation, albeit during Winter.
JMO