They did the same mistake as George Lucas did, making up the movies as they went along and halfway through writing the next one they tried to come up with "good ideas" that would blow people's minds the same way "No, I am your Father !" did back in the day.
So in an effort to catch the Promethean lightning, JJ Abrams started the ball rolling with his goddam awful "Mystery Box" Setting everyone and everything to be a big mystery that will blow your mind. Who are Rey's Parents ? Who is Snoke ? Will Finn survive ? Will Rey redeem Ben ?
The problem with his stupid mystery box is that you give that typewriting monkeys collective known as the internet, all the time in the world to come up with their own answers and odds are you bump into a tweet that either nails it or even comes up with ideas that makes you ashamed to call yourself a writer.
In an attempt to salvage this worm-riddled green stoolwater of an idea, Johnson tried to subvert our expectations by defusing the reveal, she's not a secret Kenobi, she's not the reincarnation of Annakin Skywalker who wants to complete his arc or somesuch idea, she's just a nobody that happens to be strong in the force, not entirely uncommon given that we had a whole council of people strong in the force working together as the Jedi Council. And we did establish that both Annakin and Luke could use the force instinctively or with a minimum of training (five minutes waving a lasersword at a drone, getting some encouraging words from a dead guy, focus and get your lightsaber out of the snow or merely participate in pod racing)
Snoke isn't Plageis, or Darth Onthenosemynameis etc.
Points for ideas, major demerits for execution.
To make Luke a failure must have sounded awesome at the brainstorming session, when somebody proclaimed this movie writes itself, they all high fived and had pizza before giving it to the intern to type it into a script by next morning.
George Lucas also had similar flashes of frown-inducing ideas : Leia is Luke's Sister !!! Or write the sequel in such away that Obi Wan sounds like a maniac when he remembers his best friend, the guy he amputated of most of his limbs and left him to burn alive, not even have the decency to give him a quick and merciful death for the sake of that friendship you seem to be all so upset about. And remember they had to CGI him picking up the lightsaber in post because George only works from memory apparently. And I'm not even starting on the ridiculous convoluted, riddled with risky assumptions plan by Statler and Waldorf to bet on the kid of the guy who just destroyed the Republic, completely ignoring the girl and let him grow up just as frustrated and volatile as his dad. Way to go wise jedi master Yoda !!!
So at least we are keeping that tradition alive.
Personally I felt Luke's failure kinda ruined all that they had achieved in the OT and had been building up since the Prequels. Now the story of Annakin's redemption is somewhat iffy, does killing the Emperor really make up for all the murder Vader did over the years ? Like I said, Lucas made it up going along and never looked back to make a simple check.
But that endless cycle of seeing somebody fall to the dark side is the curse of Star Wars films, it's the 
ing default story, just like people won't learn to put an "out of order" sign on the holodeck to prevent it become sentient or trapping people inside or whatever they need to fill out a season.
The biggest mistake is that Disney thought they had bought a property they could milk for all eternity, but it's one stupid story about space wizards and laser swords that got out of hand. Marvel has over ten thousand characters, that's ten thousand potential stories, not counting all the crossover potential. Sure some will fail, but but you're not at square one when your tentpole blockbusters fail to make a profit because people get tired of the same old story over and over.
And now that we are back to JJ Abrams for the next one, expect some serious retcon and some ing stupid unresolved mysteries promising us another round of trying to hit the drone without the force …
looks at some new terrain products, which use space age technology!
