Why? It was Superman territory long before Green Lantern was even created. He's always going to be based in Metropolis, but after all these movies, we need something new. Donner and Smallville handled his emotional progress, what else is there to know? Donner showed where all his influence and personality came from, where the suit & symbol came from, when he was sitting in that pod getting lectures from his father on why he was sent to Earth in the first place. We then saw him interact with his surrogate parents where he got further knowledge on how to be a good man. Its not like Donner or Smallville are the end all be all, but my point is that the topic has been touched on quite a few times, audiences need something different other than Clark feeling alienated, saving Lois from faling somewhere and fighting Lex Luthor, again.
Because if you start doing that in Superman, then Green Lantern becomes redundent. Why did The Dark Knight do so well? Because it wasn't just a Superhero movie. It was a police drama with superhero characters in it. It staked it's own claim. I think all superhero films should do this.
Wonder Woman-Large Scale Fantasy
Green Lantern-Intergalactic Space Opera
Aquaman-Swashbuckling High Seas
Superman-Invasion/Disasters
Superman has always been at his best knocking around some super powered baddy in the skies over Metropolis. Just because he HAS gone to other planets doesn't mean that is where he should stake his claim in films.
And no, there is not emotional journey in Donner's films. Clark Kent is a good person through the whole thing and doesn't grow or really respond in any way to the situations around him. How can someone raised to be a simple man REALLY comprehend everything that he is becoming, a savior, a GOD to some. What does that do to him emotionally, how does he grow? We never see it, we just show that at one point he is a teenager who kinda shows off but not really, then he is a grown up wearing bulky clothes at one time and spandex at the other. We don't see him get the suit, nor do we get any real explanation. We ASSUME things but those are called plot holes and aren't good film making or story telling.
He does grow in Smallville but it's one step forward, two steps back. He is spending too much time whining to believe that he is anywhere NEAR becoming Superman.
No one wants a long, drawn out experience on Krypton (though maybe a direct to video DC Universe Animated prequel showing the history of Krypton ala Gotham Knight would be a cool addition.) We want to see character development. Make us CARE about Superman. I don't just want to see him lift and punch stuff for 2 hours. I want to see him grow, learn and progress.
People worry that Superman isn't relevant anymore...well then MAKE him relevant. Not "darker" but more personable, more relatable. Not flawed, but an actual character, not a plot point.