Internal heaters are rare on commercial washing machines
Ever since the days of "steam laundries" places used steam to heat and or boost water temps. It just makes more sense since the plants already had power plants making steam that did everything from heat water in boilers to provide same for ironers, irons, presses, dryers, starch and soap cookers, etc....
Steam was also used to run engines that turned the belts providing motive power for all sorts of equipment. That and or depending upon the facility steam ran the generators which produced electricity; the "excess" or "waste" steam used after that work was done went onto heating purposes.
Beauty of steam heating in washers is you don't have immersed elements that become encrusted with hard water minerals. Also if one recalls correctly from high school physics steam provides greater heating power than any other source; hence it being used in a wide variety of applications.
If one had the room, money and space would love to have that Wascomat set up. That thing while vintage with proper care and maintenance would likely still outlive us all.