Answer: They are both celebrating a 50th anniversary.
Here's the release:
"Beginning mid-April, Princess Cruises will partner with Twentieth Century Fox Home Entertainment to screen the biggest movie musical of all time, The Sound of Music, onboard all 18 of its cruise ships and feature sing-a-longs, trivia games, and other movie-themed experiences throughout the year. The offerings celebrate the 50th anniversaries of both the cruise line and the musical and are part of a year-long campaign to honor the classic film.
