Why do people hide in bathtubs during tornadoes?

If you do not have a basement or storm shelter, a bathtub is probably the next safest place in your house to take cover. When a tornado is coming, the basic idea is to put as much between you and it as possible. Since bathrooms are usually small rooms, the walls are less likely to collapse than in a living room or kitchen. The bathtub itself adds another layer of protection to the sides, mainly against debris. Objects that fall may fall across the tub, rather than hitting you. It is not as good as a wall, but it is better than nothing.