Theory: It's mostly because of Warner.
During the mid-2000s, People outside of comics knew that the top five Justice League members are Superman, Batman, Wonder Woman, Green Lantern, and Flash. The only problem was that they knew them as Clark Kent, Bruce Wayne, Diana of Themyscira, Wally West (aka Funny Flash ), and John Stewart. There was no need to alter their personalities because the Justice League cartoon had set up a fun dynamic for these five.
Around that time--before Warner was starting to think about taking advantage of their superhero properties--DC decided to push Hal Jordan (I'm guessing because Didio and Johns missed the character). Around this time (pre-new 52), Johns wrote Hal without a personality which allowed people to imprint themselves on the character. This and the fact that Johns established a sweeping epic made Hal Jordan DC's 3rd highest selling character--even though any human GL could have been used in his place--but I'll save that for another discussion.
Anyhoo, let's flash forward to the later 2000s. The Justice League show is over after having reached hundreds of millions of viewers, and Warner starts taking comic book properties more seriously. They decide to start mining their popular properties other than Batman and Superman. Based on sales figures and a push from Johns/Didio, Warner decides to build on the GL property. They release Hal Jordan movies on dvd that do moderately well, so they greenlight a live action film and an animated tv series. Only problem is that Warner realizes that Avengers is going to make gangbusters. So after the GL flop, they tell Didio and friends to start developing the JL property.
This leads to major changes in the comics. GL on the JL can't be John Stewart anymore because Hal is their 3rd highest selling character. But now DC needs a popular Black character so that when movie audiences see the movie, they won't think DC is racist for making GL White and having an all White JL. Key Cyborg's entrance to replace the least profitable JL member.
To make the kind of money Avengers made, DC has to make the comics easier for studios to adapt. Johns works on flushing out the Aquaman property more. The Wally Flash is replaced by the Barry Flash because his origin is simpler to adapt for a movie. But Barry is not at all known for being a Spider-man-type Joker the way that the cartoon Flash is. And this changes the popular team dynamic--plus you need a joker on every superhero team to lighten the tone and to remind audiences not to think of the story as happening in the real world.
Barry doesn't have a history of being a Joker--but Hal does. He was a funnyman in the Bronze age of Comics. So Hal's jokey trait is played up more in the movie and in the book. This wouldn't be a problem if he weren't written as a giant douche.
What does that mean for us fans? We get Hal Jordan and Cyborg pushes like this:
And it will keep happening now that Warner is eyeing a JLA film for the next decade.
How could it have turned out differently? If Wally outsold Hal or if DC pushed John Stewart instead of Hal in the mid-2000s or if people didn't care about diversity.
Just my theory.