I've had this on a few ships. I really think some of it just has to do with the elements. The windows get washed frequently, however the splashing salt water doesn't shop. The harsh environment just eats at the metal and paint leaving signs of rust. Having the quick turn around after each voyage doesn't lend itself to treating each inch of the ship all the time, and if they said to everyone stay off your balcony for 6 hours while we power wash the ship in port people would complain.