The Carnival class is a luxurious homes away from home. Liners are built to look fast and grand at the dockside. Not just the reputation of your service but the image your ship projects is important. You need that impressive beauty ship for the advertisements.
The Carnival class will take 500 passengers and an equal number of crew. The Whimsy has fewer crew as many of the crew on a standard liner are Entertainers. This is the whole point to Fuzzy, and they do not carry paying passengers. The ship is seldom full.
in 2380 Fuzzy took a two year hiatus while the SS Whimsy was refit to the latest standards and got disodium warp drives as well. Not generally available at the time. Due to greater speed they have broadened the circuit to take in more of the Federation than they could before.