Why might film makers or directors try to make the main character more likeable in the film than than in the book version of the story?

Because authors usually tell the reader the main character's thoughts, the reader can empathize and still support the main character. In a movie, however, the audience doesn't get the "backstage pass" to the main character's thoughts. In order to make the movie more appealing, the filmmakers need to make the main character more likable.