All very well, but if there are problems with the machines and demand is high, you cannot assume that you can saunter down there with your washing and that a macine will be available.
Furthermore, it is not at all unusual to find that there is a machine idle, but still full of clothes! Apparently some people can get very upset if you empty their finished laundry out of the machine.
Staff and crew, right up to the Captain, are fully aware of the disputes that arise in the laundry.
I'd suggest that if you want to enjoy a relaxing holiday, and if your cruise is one of only 12 days, wash stuff in your room, and pack sufficient to cope for your holiday without the need to use the laundry room.
But, having said all of this, we always take a suite, and our loyalty level means that we never need to use the laundry!