They probably can be but the rub is that they would be a lot louder...we have a new dishwasher that is so quiet that you have to concentrate to hear it even while standing in the kitchen within a few feet (only noise if makes is when it drains - can hear it in the sink drain)....it supplements the cleaning cycle with steam and we’ve had one bowl that had some crystallized candy stuck to it come out less than pristine - big bowls top and bottom blocking some of the flow probably helped.
They are quiet, but so was the one we bought in 2007 when we built a house in Illinois, but before the full force of the regs kicked in. You don’t need a government regulation to get people to buy quiet dishwashers. Some might even have a quiet vs. fast setting. We might see that we the new generation of fast dishwashers. Now I am waiting for making washing machines and toilets great again.