The Airbag Car

Why are cars still made of steel when airbags have been shown to be so effective? Why not make a car that is all airbag? The occupants would be surrounded by airbags instead of metal on all sides. We're moving that way anyhow with front and side airbags. Why not go all the way with the concept? Airbags inflated everywhere except the bottom and the front window. Forget the sheet metal entirely. It would be a very light vehicle and get high fuel economy. If you hit anything, or got hit, you would just bounce. It worked for the Mars explorer. It could work on the highway.