User blog comment:HiccstridFan92/Handling Spoilers for the Third Film/@comment-27624304-20180524233558/@comment-244709-20180525145628

The different release dates are all related to marketing. Really interesting article here about why Marvel does the same thing with their films. In sum, they take note of international holidays, which are definite banking dates for movies; they implement previous strategies in releasing overseas to create "international buzz" and momentum for later releases, including U.S. ones; and they sometimes use other countries as "test groups", typically for deciding whether or not to add "last-minute additions" or changes to the film.

The goal with this kind of marketing strategy is to maximize box office profits, and these are the things taken into consideration when trying to do so. DreamWorks and Marvel are just two of many other film companies that do the exact same thing. Not completely sure if Universal had anything directly to do with HTTYD3, but it wouldn't be surprising if their marketing team is the one calling the shots. Again, this marketing strategy isn't a new thing at all, and Universal has lots of experience in marketing films.