The Dutch spag is dead-on... I would bet money that not one single person actually pulled out their phone WHILE Nye was down. There's a mass paralysis that happens in situations like that, which makes actually doing ANYTHING but gawking kind of impossible. Interestingly, though, once one person does anything... literally, anything... it breaks the spell and people can act. You can actually do it just by shouting "hey" or standing up, if you have the presence of mind for it.
There's a corresponding trait in humans, too, which is that once one person helps, a lot of other people will be galvanized to help as well. Actually, a lot of multiple-drownings happen that way, unfortunately.