This is funny. Actually a lot of my friends do this when playing also. My idea to why this is done is because they are thinking about their next shot and not about the placement of the chalk. If you notice most of the time when players put the chalk down they are not staring at where they are putting it because their eyes are on the playing field and focused only on that.
I agree. I've tried to kindly explain to players just like it was explained to me. Well I got more of a scolding when I entered my first pool hall from the owner.
I've even wiped down the table and placed the chalk blue side up every turn at the table.
Ya can't change the world.