The exterior shell is because it aluminum. Go figure less durable than fiber glass. Easily dented as well. You wouldn't think but the Alcoa clear on it isn't that good and degrades if you don't keep it waxed and protected from the elements. Ceramic coating is an added insurance policy and less to maintain on the outside. Just normal washing needed. Everything beads right off it. The more important thing is you don't want to let the finish go to where you actually damage the aluminum finish and is then irreversible and expensive as you need total panel replacements. That damage is called filaform corrosion or oxidation. Salt exposure is really bad for it.
Have you ever seen one in person? I had same thought process until I stepped into one. My wife wanted it and we all do what we can to keep the wives happy

. I was against the investment initially quite honestly because of the exorbitant cost. The interior is first class. Top quality construction and feels that way when you are living inside it. What sold me is that they hold their value incredibly well. Better than any other RV in whatever class you look at. They also last for generations if properly maintained. Maybe I'll pass down to my kids. Who knows. Some also say it's pretty neat to be a part of the AS and Wally fan club. It's a cool community that everyone sticks together and share experiences. It's pretty nice. I relate it the the Ducati owners and many friends I hang with that own the brand.
I did some heavy upgrades to it in the 2 years we owned it as well. Solar, lithium, multiple inverters, 4k TVs, blah blah blah. Too much to list. Can boon dock for weeks at a time if I want.