Earlier quoted context omitted.
Maybe I should make the obvious reason more explicit. If you have something designed to operate on 120V and plug it into a 240V outlet, there will be safety issues. It might even catch on fire. So the two voltages have to use different outlet and plug shapes for safety reasons. An outlet is not “randomly” going to be one voltage or the other because that would be a terrible idea. And yes, the 240V outlets are set up…
I think the main speed increase of American machines compared to European ones is due to much higher water consumption. A modern European washing machine uses 30-50 litres per wash, vs 75-100 for a modern American one. That's also halved the time required to heat the necessary water, so another reason a hot water connection might not be so useful
Maybe we just have bigger washing machines? You need to control for washer capacity to make a fair comparison here. If you need to do twice as many loads of laundry because you can only fit half as much laundry in each load, you’ve gained nothing. And it’s not like having a bigger washing machine requires every load of laundry to use the full water capacity of the machine even if you only do small loads. On older machines you can set a dial for load size while newer ones have sensors for that.