cruise ship construction

Why is it that modern cruise ships become "rustbuckets" in only 15
years?!
Are they poorly built or poorly maintained?

I say BOTH!

Many ships built in the 80's and 90's have STEEL water and drain
pipes. They rust out in 12 years. Where does that leaking water go-
especially the pipes hidden in the walls?! Are they still using steel
pipes in new construction, instead of pvc, hpvc and copper?

Many of the laundries have NO drain pipes, in case a poorly maintained
washer hose breaks. I've seen 5" of water in a laundry room before.

Am I the only one who ever smelled sewer gas throughout a cruise ship?
That's due to not cleaning out the drain pipes regularly. It's also
due to poorly maintained or no water softening equipment.

Cracking and breaking of poor quality calk around upper (outside) deck
water drains. Where does all that water go that seeps into those
cracks?

Makes me wonder what else is deteriorating behind the walls of cruise
ships.