How much more efficiency would be gained?
The makers have been working diligently on efficiency since the 1970s.
A lot of those “energy efficient” appliances aren’t. I forget exactly, but something to do with the watts/hour that they use.
So to get the numbers down, they use a weaker motor (say your washing machine) and run the wash for longer. Less watts/more time gives it a “good” number. I guess the manufacturers don’t mind the rules as the stuff wears out quicker and you have to buy another one sooner.