And furthermore, if I just have two dishwashers, both of which are considered "dirty", I no longer have clean plates.

Unless, of course, I unload it to the cabinets. Which I do now. Without paying $800 for a second dishwasher.

No, it's probably about three-quarters empty, because you probably use roughly the same crockery every day, unless you do something particularly bizarre like having three soup-based meals one day and three plate-based meals the next. Sometimes you wash a couple of plates that were already clean, sure. Or you move them into the "clean" dishwasher before declaring the other one "dirty", which is no more effort than putting them into cabinets (often less). And sure maybe a couple of days a year you have a big party, or really do eat soup every meal, or something, and you have to do something different. But the vast majority of the time it makes life easier.