It looks like you mean Star Wars: A New Hope , and Lucasfilm didn’t “decide” to name the original film that until 1979 , when the movie was re-released and the subtitle was added to distinguish it from the expanding saga.

What happened

  • The film was originally released in 1977 simply as Star Wars.
  • The title A New Hope was added later, during the 1979 re-release, after the sequel made it necessary to separate the first movie from the broader series.

Why the change

  • The new subtitle helped frame the movie as part of an ongoing story rather than a standalone film.
  • It also made room for the franchise to grow into a multi-film saga.

TL;DR

Lucasfilm added A New Hope in 1979 , not at the original 1977 release.