Because, though the titular characters are absent for most of those films, the main characters (Dorothy and her friends/The Nostromo crew) have enough development and chemistry to keep our interest instead of complaining about the lack of Wizard/Alien. This cannot be said for the Transformers movies where the characters are nothing but exposition and joke spouting set pieces. Each Transformers film has three character archetypes: - Serious - Humor - Eye-Candy Annnnnd, that's it. Most of the performances are shallow and lack emotion. It's simply maddening to say they're on par with the cast of Wizard or Alien.