They have not always existed and seatbelts alone were not enough to protect the head, especially on 70's/80's cars were the direction column would often be pushed straight in the direction of the driver when the cars smashed something.
Even the motorcycle helmet laws didn’t start to to into effect until the 80s/90s. that was about when airbags started getting added to cars so they were roughly parallel efforts along slightly different lines.
Essentially the car becomes the helmet and does a more complete job on the whole body than just the helmet on the motorcyclist.
