Bag Ladies

What is it with students and their bags? Students have to put their bags on their chairs so they perch on the front half of their chair with the bag propped between them and the back of their seats. It doesn't matter that they could put them on the floor, or on an empty chair, or even on the table; most of them put their bags on their chairs - and I don't mean hanging from them.

I mean, this is a classroom and in Japan. It's hardly likely someone will come and swipe their bag.

I don't get it.