Not sure who the "they" is. I just looked at the tag on the Breville electric kettle sitting here. It says 1500W, right next to the UL listing. Would I prefer that our homes used 240V instead of 120V so some small number of appliances like this could benefit? Sure, but I don't think that's going to happen.
And it gets there much faster with half in the electric kettle, which adds another 1.5KW to the process.