While that is no doubt good advice when possible, it's not always possible or desirable. Sometimes the other parts of the vacation are other cruises, with perhaps only one or two nights between them, which makes it a challenge to wash and dry clothes. It's much easier to do so during a cruise because there are typically more consecutive nights on a cruise, and because it's a lot easier to put a load of clothes in the machine, grab something to eat or drink, come back to the machine, etc. As far as using Airbnb's, I'm also somewhat hesitant to use those in other countries. I prefer to use hotels.
Note that I'm not trying to say that everyone should wash clothes during a cruise. Of course not. I'm just trying to explain to those that say basically, "don't wash clothes, you're on vacation" that there are a lot of factors to consider.