I'm going to Devil's Advocately defend their decision to do this trilogy with no plan. It was obviously was a completely disastrous failure in implementation, but I can kinda see how they arrived at the decision to do the sequel trilogy this way.
Basically, they're trying to make a new Star Wars trilogy. What's the essential ingredient of all Star Wars trilogies?
That's right: George Lucas making everything up as he goes along, then lying his face off and saying he had a plan the whole time.
The results of this creative process can be quite lovely, especially when George Lucas's powerful creative and directorial vision is harnessed and channeled by someone with authority over him. My (limited) understanding is that A New Hope is as much Marcia Lucas's film as George's, and that The Empire Strikes Back is as much Lawrence Kasdan's as George's.
So you let really creative, talented artists into this playground of George Lucas's mind, you see what they come up with, and then you pass it off to the next guy to riff on it some more. Star Wars is poetry, sure... but really great Star Wars is
scat.
This creative churn can really augment the original plan, even if the original plan is pretty good. We see that happening in the evolution of the original Star Wars trilogy, we see it in the way DS9 had a vague plan but kept incorporating new elements into it as the writers discovered them, we see it in how (CONTROVERSIAL TAKE) Babylon 5's rigidity kept it from achieving its full potential, and I've seen it myself in making
my own show -- various other writers for my show have contributed ideas that have led to drastic improvements to the original series arc. (Abrams gets all this exactly right in that interview.)
So I'm thinking that Disney was thinking, "We're not going to rely on one static brain to deliver one trilogy with a single unified vision like LOTR or the prequels or the rigid destination of the Marvelverse; we're going to embrace Star Wars's happy-go-lucky attitude, make like the Original Trilogy, and
improvise!"
It could have been amazing.
It wasn't.
Four reasons I think it failed:
1. They didn't have George Lucas. Sure, Marcia Lucas saved ANH in the editing bay. Sure, Larry Kasdan saved Empire by being great. But George Lucas was also essential -- he
did have a (vague) central vision and forced his co-creatives back to it. This moderate tension created balance in the force -- the movies couldn't go too far into Lucas's weird proclivities OR go too far off the rails from external pressure. Get rid of Lucas, though, and there's no core of continuity through the full trilogy. (On the other hand, get rid of the outside perspective, get rid of the people who can say "no" to Lucas, and Lucas ends up running everything. That's how you get the prequels. Disney's plan here could be seen as an overreaction against how the prequels got made.)
2. They hired JJ Abrams to establish the future universe. Abrams is good at characters, good at teasing, horrible at worldbuilding, and his plotting is mostly rapid-fire spaghetti with jokes. His Star Wars was a mess. A fun mess, but not a universe that was easy to build onward from.
3. Johnson was apparently given
zero ground rules, and nobody bothered to confirm that he actually
wanted to make a movie building on Abrams' movie, and was thus allowed to reject the heart of
The Force Awakens. As anyone who watches improv comedy knows, you can't do good improv by trying to override a bad audience prompt or a weird direction your fellow performer takes it -- you have to follow it and try to build on it, maybe gently draw it back in a more amenable direction. Johnson didn't. He tried to raze TFA and build his own thing instead.
3a. Instead of hiring a third director to try to build on the other two movies and draw them together into a healthy conclusion, they re-hired Abrams, who spitefully razed Johnson right back, so all three movies in this trilogy are at war with each other. That's not improv, it's just ugly.
4. They also didn't give Abrams enough time.
4a. Also, Abrams is terrible at endings and everyone knows this, so what are you guys doing?!? (Answer: they were too cowardly to take a risk on, say, Lorde and Miller and too desperate to meet the deadline to wait for anyone else.)
There is a version of the sequel trilogy out there, floating somewhere in what Russell T. Davies calls The Maybe, which is both 100% improvised with no plan and the greatest set of Star Wars movies ever. But that was not the set of sequels we got, because even an unplanned trilogy needs an assertive consistent creative vision (like George Lucas, apparently unlike Kathleen Kennedy), it needs the ground rule that everyone needs to cooperate and build up not bicker and tear down, and it needs to not hire a terrible endings-man to write the ending. Improv is always a risk, but they set themselves up for failure in a big way here.