One advantage of keeping it behind the windshield (aside from having a higher point of view), is that they get automatic camera cleaning from the windshield wip

One advantage of keeping it behind the windshield (aside from having a higher point of view), is that they get automatic camera cleaning from the windshield wipers (plus defrosting). If they put it lower behind the grill, then they need a completely separate cleaning/defrosting system. My car's lower bumper mounted radar antenna stops working any time I drive in the snow because it quickly gets coated with a layer of snow.