They were safer as well; having the controls high up in the backsplash made burns from steaming pots less likely. This was one reason CU loved Frigidaire stoves in many reports. English electric stoves have the controls at eye-level for convenience and safety. Also, controls farther away from small children's hands.
It's easy to see how high controls disappeared after a while especially from the greedy-corporate perspective; all that extra metal and porcelain cost money. My favorite GE stove from the late Sixties sported high controls when they finally moved the burner controls onto the backsplash where they belonged:
Well, kitchen cabinet and countertop lines changed as the modern lines of the 50s evolved and cabinet ranges tried to look more like the builtins that became such signs of desirable modern upscale kitchens.
The taller the appliance, the bigger the box needed to ship it. Also the more packing materials. The more space it takes up during shipping. The more space needed in the warehouse.
Though I've seen a couple of those double oven, free standing stoves from the 60s and 70s, I never had to deal with them.
I don't know if they come apart or if they literally shipped them in one piece.