Toggles, many, if not most homes built in the 60s had the power for an electric dryer because, at least in the South, the newer building codes called for a minimum of a 150 amp electrical service and circuit breakers, not fuses. The fact that large areas of the Southeast were served at least in part by the Tennessee Valley Authority with a great deal of cheap hydro-electric power helped too. The TVA came along in the 1930s with the Rural Electrification Association and those two agencies transformed life in the poverty-ridden areas of the Depression era South. When my parents finished off part of the basement in our 1955 ranch style home as a studio apartment for my brother and me after our sister was born, the heavy up was almost free from Georgia Power if you bought either an electric range or dryer. I guess if anyone was stupid enough to switch from a gas to an electric water heater, it would have qualifed also. It had to be a 220 volt appliance that would be used all year so air conditioning did not qualify, but a heat pump would. The builders were either installing central air in upscale homes or knew that window units would be installed so that was another reason to have an electrical service with some extra capacity. A lot of homes were being built as total electric "Gold Medallion" homes even in places with a natural gas supply. Ah, to go back to the days when we were encouraged to find more ways to use electricity and no one voiced concern about demand exceeding capacity. Older homes in towns that had gas supplies had gas dryers if they did not have the capacity for an electric dryer. There were the home handymen who did their own wiring and arranged to have 230 volt air conditioners (the norm back then) and an electric dryer with instructions to the family to only use one ac unit when the dryer was in use. Laundry was done early in the day when it was cooler and it worked out if the house only had a 60 amp electrical service and a gas stove. By the very early 60s, at least where I grew up, new homes came with a 220v/30 amp dryer outlet in the laundry area. This was also the time when GE had a real lock on built in kitchen appliances because they would practically give the builder a built in dishwasher for about $10 with the purchase of built in electric cooking equipment. A new home with a kitchen that included not only a built in cook top and oven, but also a dishwasher, made a much better showing to people wanting a new home with modern features. The electric range and dryer outlet won the builders some breaks from the power companies also, so it really paid to make homes ready for electric dryers.
With the long drying times of a 115 volt dryer, new construction, remodeling, installation of air conditioning and other reasons for improved electrical service, not that many 220 volt dryers had to operate on 115 volts before the house had enough capacity to operate the dryer on 220.