Well, since I have no work right now :-(
I think the most obvious answer is "Because the screenplay required it". That's the way the sequels often play out. Stuff happens because they need to happen to move the story forward - instead of actions coming out of characters and things developing logically.
Leia being a Jedi specifically though.. I bet you they read reviews and criticisms and decided to 'retcon' the sequels to shut people up. So when people complain that Leia could Mary Poppins her way to the ship in outer space, and also complained that Rey is Mary Sue, they found a solution in making Leia a Jedi retroactively. Like every other 'solution' in this trilogy it creates more problems than it solves, like you pointed out. It's just shitty writing.
I think they could have made it work if Luke was the very last known Jedi and he went into isolation because he didn't want to teach anyone and have them fall to the dark side, and then they learn that someone has "spawned" or they forgot to count someone or whatever. But of course again this 'idea' in the story means that Luke would have turned his back on Snoke and Kylo and others despite being the one who defeated Anakin and the Emperor. Shit writing.
"The script required it" for all of the above. So much stupid in that section of the film. Horses on a Star Destroyer? We don't really need to know anything else, do we?
Shit writing.
For anyone who's bored:
When did Leia become a Jedi? Did I miss all of her training? If she was a Jedi, why did she never fight or even carry the light saber in all 9 movies, the weapon of the Jedi? And why did R2 have to send that urgent message to Ben Kenobi, 'our only hope,' back in IV? She was a fucking Jedi! Has any other living Jedi still involved with the Rebellion (so I'm excluding Luke) ever given up her lightsaber?! I get that she became a Commander/General/whatever, but why give your lightsaber to your brother, to hide under a rock?
I think the most obvious answer is "Because the screenplay required it". That's the way the sequels often play out. Stuff happens because they need to happen to move the story forward - instead of actions coming out of characters and things developing logically.
Leia being a Jedi specifically though.. I bet you they read reviews and criticisms and decided to 'retcon' the sequels to shut people up. So when people complain that Leia could Mary Poppins her way to the ship in outer space, and also complained that Rey is Mary Sue, they found a solution in making Leia a Jedi retroactively. Like every other 'solution' in this trilogy it creates more problems than it solves, like you pointed out. It's just shitty writing.
Luke is the badass of the universe through IV, V and VI and then we find out he hid on a desolate planet because he was scared? Waitwut? It would have been better to say that he was afraid if himself and giving in to temptation, but Abrams neuters Luke by saying he was scared and just leaving it at that.
I think they could have made it work if Luke was the very last known Jedi and he went into isolation because he didn't want to teach anyone and have them fall to the dark side, and then they learn that someone has "spawned" or they forgot to count someone or whatever. But of course again this 'idea' in the story means that Luke would have turned his back on Snoke and Kylo and others despite being the one who defeated Anakin and the Emperor. Shit writing.
And we have this tower that controls an entire fleet. But the Rebels figure it out and plan to destroy it. So the the First Order switches to the command ship for control (uh, what? Doesn't that command ship need the tower for orientation?!), the Rebels just abandon destroying the tower when all it would've taken was one blaster?! Not to worry, though, because when the Rebels switch the attack to the command ship, no one in the First Order thinks to switch control back to the undestroyed tower... And why the fuck wasn't that tower better protected? And better hidden? And why weren't there multiple towers? No one ever heard of redundancy, especially when dealing with such a large fleet?
"The script required it" for all of the above. So much stupid in that section of the film. Horses on a Star Destroyer? We don't really need to know anything else, do we?
Why did Rey have to bury Luke's lightsaber there? It was just a convenient reason to get her to Tatooine so she could declare herself a Skywalker and renounce her Palpatine bloodline, even the the whole movie was about not being afraid of who you are (and the whole point of all nine movies was overcoming who you are). So rather than redeeming the Palpatine surname, she switches to Skywalker. Why, so the movie title makes sense?
For that matter, Rise of Palpatine would have been a better title (except that Palpatine was dead), leading the viewer to wonder if the First/Final Order was finally gonna win. Maybe that would have been better if we didn't know this was the last movie. And it would've spoiled the reveal that Rey was a Palpatine, except that you knew that as soon as she shot lightning out of her hands in the first what, half hour?
Most importantly, who would fuck Palpatine?!
Shit writing.
For anyone who's bored: