The Girls Died because the Dark Side was strong in them...

After watching this movie again after some time, I think the unanswered questions surrounding the girl's deaths are summed up quite easily when you put 2+2 together.

Hayden Christensen was one of the homecoming dates. If you look closely, he seethes Dark Side all over the girls during their drive to the dance, and obviously on the way back home. The Dark Side slowly began wrapping smoky tendrils of darkness around young-girl brain stalks, and after quarantine, the darkness was simply too much for them to bare. It dominated the girl's wills, spiraling them into a world of fear, hate, suffering, and unto their ultimate doom.

In the end, Anakin Skywalker claimed their lifeblood. His infamous legend only grew onward from there...