A suggestion

Rating: 1/10 (11 January 2018)

I didn't like much about The Last Jedi, mostly due to bad storytelling, a bad script and unclear characterisation or missing backstories to explain it.
Just to illustrate, that it isn't all that difficult to come up with a satisfying and logical backstory for the characters in The Last Jedi, here what I would have come up with:
After "Return of the Jedi" Leia and Han decide to settle down while Luke starts building his Jedi temple and rebuilding the Jedi order. Leia gets pregnant and as it runs in her family, gives birth to twins, as you might guess, Ben and Rey. One of the babies gets abducted which leads to a desperate search over several years to find their lost child... without success. This of course is too much stress for Han and Leia's relationship and they seek comfort in their jobs. Leia turns back to politics and Han starts roaming the galaxy with Chewbacca in the Falcon again. Meanwhile Ben feels unloved, because all his parents' focus lies on his lost sister. But because the force is strong in him, he is sent to a boarding school - Luke's Jedi temple. There his uncle tries to keep the hurting boy on the right track. Everyone thinks this is the best decision, but ultimately makes Ben feel even more abandoned by his parents and he starts turning to the dark side.
In order to not spill all my beans as a director yet, the first part of the story, would be revealed later in episode IX. You may ask now, why Leia doesn't recognise Rey immediately when they reunite in The Force Awakens? Firstly because Leia only knows her daughter as a baby and secondly because she feels the connection, but doesn't want to go down this dark chapter of her life again before being absolutely sure. Maybe she also hopes, Luke will help to clarify if Rey really is her daughter.
Now the reveal for The Last Jedi:
More and more younglings seek training at Luke's temple, as the force "reincarnated" in many babies born after the extinction of the original Jedi order. Luke needs help in training all these young people from all over the galaxy. He feels a strong presence, decides to check it out and finds Snoke, a strong Jedi who was stuck since the Clone Wars alone on an outer rim planet, with no means of transport to get back to the more densely populated areas of the galaxy. (Of course this is a lie: He was hiding there on purpose, waiting for his time to come, strenghening his power of the force. )
Snoke now trains half of the younglings, as Luke does with the the other half. This is how Snoke gets close to Ben and ultimately corrupts him and other pupils to the dark side. When Luke senses the danger it's too late: A fight erupts and while Luke manages to fight off Snoke and disfigures him in the process, he doesn't know that Ben has been corrupted too or simply doesn't want to believe it. Ben force pushes him off a cliff and Luke falls to his presumed death. Snoke and Ben slaughter all of Luke's younglings, destroy the Jedi temple and head off to take over the remains of the Empire with the help of their group of younglings to form the New Order. Luke which survived the drop, despairs of having failed Leia, Han and Ben, his younglings as well as the galaxy by not being able to rebuild the Jedi order and therefore restore a safeguard for the galaxy.
In the end we are at the same point: A lonely Luke on his island, an emo Kylo Ren and a sadened Leia, but with a backstory about Rey's parents, as well as a backstory for Snoke at the same time. It also explains why he killed his father, but couldn't kill his mother: He felt more abandoned by Han thus hating him more. His mother was at least around part ot the time, when she wasn't travelling the galaxy on political missions. 2 simple flashbacks and everything would have made so much more sense and the characterisations would have been clearer. Maybe this little nerdy fanboy theorie is too simple and a good writer could spice it up and add some twists, but I normally don't write fan fiction, I just wanted to illustrate that it's not that difficult to come up with solutions that don't involve the attempt to murder a nephew in his sleep.