As for Karajorma, I wasn't aware Rian Johnson had publicly complained about the backstory being unavailable for him. Unfair yes, but it doesn't matter in the end. That statement also means the story line was open and he HAD the time to fill in what he needed for the second installment. He could have left parts of it open. Instead he chose to wreck it all, invalidating the point of watching the first movie in the trilogy. Now this really is quite unprofessional and amateurish, and this in a series of movies famous for their continuity! Did he really even spare a second of thought to what it would do with respect to the general reception of the trilogy? Besides, what did Disney ask Abrams to do? Direct the first movie of a trilogy is one thing, but what does that contract say about the entire story line? If it wasn't part of his contract, there's your answer. And having seen enough corporate BS for my life time, I wouldn't be particularly surprised if this actually happened.
Wrong again. JJ Abrams collaborated with Rian Johnson on the plot line for TLJ during its development. If none of JJ Abrams ideas for the contents of his mystery boxes made it into the final film that suggests that
a) He flat out refused to explain them to Rian even though they had extensive discussions during which he explained his vision of the 2nd film.
b) He knew the answers to the questions and asked Rian to leave them for the 3rd film.
c) Rian Johnson or Johnson AND Abrams decided that his ideas weren't that good and came up with better ones.
d) He had no idea how to deal with those hooks in the first place.
The fact that Rian complained that no one knew the backstory (and notice he complained about no one knowing it, not that he didn't have access to it!) means that d) is the most likely. In which case this is 100% JJ Abrams fault for introducing plot points he didn't understand. Next most likely is b) but even there, the fault still lies with JJ Abrams. You can't complain that Rian didn't reveal secrets if he was deliberately forbidden to by Abrams. If you want to blame Rian Johnson for TLJ you're going to have to prove that c) happened and that JJ Abrams disagrees with Rian's changes. Good luck!
The funny thing is you are acting like Rian destroyed all chance of their being answers to these questions. That's nonsense. Several of JJ Abrams mystery boxes are still left unopened. Luke's Lightsaber's origins. Whether Rey really was the child of nobodies or if Ren simply lied. Lots of mysteries left. And JJ Abrams is up next. So how about waiting to judge how good the answers to JJ Abrams mysteries are for when you see JJ Abrams try to answer them? If he can't do a good job himself, then it becomes even more unfair to complain at someone else not doing a good job.