It's more that a drowning person will grab anything, and if that thing is on your neck it will make the rescue more problematic than it already is. (Which is a

It's more that a drowning person will grab anything, and if that thing is on your neck it will make the rescue more problematic than it already is. (Which is also why the lifeguards here are told to approach from the side, less likely to be grabbed on the head that way.)