I was surprised by the number of bibles too! I don't think I've ever seen one as litter (not counting those left in hotel rooms), but I've seen other kinds of religious literature like tracts, booklets, and watchtower magazines
That's the kind of thing that people like to hand out to people walking by. Many people, if handed a booklet they didn't actually want to read, will just toss it on the ground.
As someone who has been pressured to take a book by random (mostly religious) people on a college campus, I wouldn't put the blame entirely on the person taking it.
