> I've always been wondering why they don't exist on smaller scale.

Because they need space, they need even more nasty chemicals than domestic dishwashers, they need a stack of trays to load the dishes on and a crew to load and unload them.

If you want a dishwasher which doesn't require unloading after use you can get 2 of them, one of which is "clean", the other "dirty" or washing. When the "dirty" one is full you turn it on and let it wash while you take whatever you need from the "clean" one. Once the formerly-dirty one has finished it's cycle the roles are reversed and it becomes the "clean" one.