It would actually be pretty easy to do with regular robotics (well, compared to a humanoid robot anyways). The reason nobody does it is that it takes up a ton of space which is at a huge premium in pretty much every kitchen ever.

Also like, loading and unloading the dishwasher is not that hard or time consuming.

I think this is a good point, but it ignores the idea that a human form is not the ideal (or even closet to) one to do specific and generalized jobs.