IMO, it doesn't matter how much weight someone has lost or how thin/fit they were to begin with, not everyone wants to see that.
There are a lot of things I don't want to see. Tattoos. Earrings on men. Long hair on men. Anyone over 250 pounds. Old people. Ugly people. People who wear yellow - which makes EVERYONE sallow. (In case you can't tell, I'm kidding - about some things).
Only men who look like Tatum Channing (and myself) shall be permitted on a DCL cruise ship from now on. And all the Tatum clones need to be shirtless at all times - definately dropping those dining room rules.
There is a globe worth of standards - from nude beaches and family clothing optional swimming pools in Europe to burkas in the Middle East. And not everyone who cruises has the same standards.
Me - I wear a full piece suit and a swim coverup - with the coverup or shorts on most of the time I'm not in the water. But I only get to control what other people see of me, not really how much I see of other people - as long as they are legal.