I don't have any shriveled soap here to take a picture of, if I were at my mother-in-laws house I could show you some shriveled soap. She collects it & has some that looks shamefull. It shrinks & gets cracked & sometimes even bows.
The deal w/ them sitting out in the bathroom is that they are probably not sitting out very long w/o being used & exposed to water. You never know how long a bar is going to sit around when you sell it bfore it gets used. It could sit in a shop for a couple years or a person could do like I do & stock pile soap & pull out a bar I may have had for 6 months or a year. I know I have customers that will buy from me in bulk & dole it out over the next years as gifts so I need mine to be wrapped incase it doesn't get *given* for 6,8,10 months it's still looking it's best.
When I first opened my shop I made a bunch of loaves & was slicing them as the customers requested. The loaves That did not sell quick enough began to shrivel. I assume it is the water content evaporating when exposed to air.
The melting away in thh shower refers to people that either allow their soap to sit in water or are in direct line of fire of the shower head so they get soggy & mushy.
Another good reason to wrap your M&P is because the high glycerin content attracts moisture. It will actually pull moisture out of the air & to the surface of the bar of soap, this is called sweating. If your soap sweats it will be sticky & unsellable. Some climates are more inclined to sweating than others.