Why do ships change names?
The ship could have been sold. Older ships are often sold to smaller operators.
Retrofitting is another. The ship gets enlarged and gets a whole new theme or design. The Carnival Destiny just became the Sunshine after a major overhaul. It's part of the rechristening process. She's no longer the same ship in many people's eyes, so,they give it a new name.
No big deal.
In the case of new ownership, a lot has to do with superstition. A new owner always gives a ship or boat a new name.