Why, then, did only Britain think it necessary to have 30A socket circuits in domestic properties, the vast majority of which were very small?
having read some of the old documentation from the time, and met some old electricians in the past, it was envisaged that any homeowner might have a 3-bar electric fire as their biggest load. It was equivalent in heat output to a medium-sized coal fire, allowing for waste heat up the chimney. So 13A sockets. They might put it in any corner of any room of the house. So lots of outlets, any of them capable of supplying such a load. In the other sockets they might put an electric sewing machine, table lamp, radio, christmas tree etc. So fused plugs.
A very small number of people might have had a washing machine or an electric kettle, as well as their electric fire, and they might well, from time to time, run two of these appliances at the same time. The chances of anyone possessing three such appliances, and using them all at the same time, seemed improbable. Hence 30A circuits. Which could run two big appliances and as many small one as any reasonable person could hope to own.
Remember that previously, people had been connecting electric irons to light-bulb outlets, so this was a big step forward. Also there had been a variety of different size and shaped plugs for 2A, 5A, 10A and 15A use, which if by different makers might not have fitted the same sockets, and householders were unlikely to grasp the concept of matching appliance load, plug type, and circuit rating.
Many birds killed with a couple of stones with the new system.
The square-pin fused plug and shuttered sockets had numerous other advantages, of course.