water softeners are common
When I lived in Ohio, the city water in my town had a hardness level of about 23 grains/gallon. My parents house was built-in 1954 and they had a softener installed as soon aas construction was completed.. My aunt and uncle, who lived nearby, had a softener installed in 1950. Most houses in the neighborhood had a central water softener.
So they were common in the 1950's (at least in Ohio) in hard water areas. It makes little sense to by a dishwasher with a softener and have calcium buildup in your hot water tank, bathtub, sinks, faucets, pipes.
I think that's why, in the U.S. dishwashers with softeners are not generally marketed. Why spend the extra money had have this ability on your dishwasher, for with probably the same expenditure, when you could have your whole house supplied with softened water and have clean fixtures, clean appliances and much cleaner laundry.