Sadly i think a major factor might be most are just easily misled and maybe even naive. He knew about her age and if she was young, it doesnt explicitly state in the video, he could also take advantage of that.He thought he was doing the girl a favor because of her age while planning to infect her with a lifetime sickness.
I can’t imagine how many women without fathers that get taken advantage of like this, because their mothers don’t look past the gestures.