I think the Highway safety council deemed them as a hazard in a crash. Also people were using them, and ''if it broke or came off, it could cause an accident''. Some of the knobs had a flip switch that allowed it to fold down even with the steering wheel. When power steering became the norm, they were probably destined to fall from popularity any way. I'm thinking of getting one for my lawn tractor. (No nekked lady though).
These are the same people who deemed spinner hubcaps a danger because the spinner could come off.
One of our neighbors had an evap cooler on his '57 Ford. His wife had asthma or a breathing problem of some kind. I'm sure it worked for them.