Its not a problem with plane construction but the age and wear on these planes. They are 747 "classics" from almost 30 years ago that have been thru a few owners probably and around the world. Its just like an old 1970 Chevy truck. Built to take the punishment, looked sweet when new, but when you put a million miles on the odometer and don't keep it in "mint" condition then it will look kind of ratty after 30 years....not to mention that the hubcaps might fall off!
If they'd put some more money into detailing & maintaining their planes they'd look great, but the bottom line is ........ $$$.