A lot of fans were disappointed with Star Wars: The Last Jedi. One of the main complaints that I've seen is that director Rian Johnson didn't explore Supreme Leader Snoke's backstory before he surprisingly...
... killed him off! During a recent BAFTA Q&A with the director, he explained why he decided not give us any information on Snoke and his past.
“In this particular story, it’s much more like the original trilogy, where with Snoke if you think about the actual scenes, if suddenly I had paused one of the scenes to give a 30-second monologue about who he was, it would have kind of stopped the scene in its tracks, I realized. Even though it could have been interesting, something that fans were interested in, as storytellers, we have to kind of serve what the scenes need to be."
I understand that to an extent. There are lots of other ways that he could have interjected a backstory. Hell, the movie could have started out with a backstory much like The Lord of the Rings: Return of the King started off telling the back story of Gollum. But the director opted just to ignore it.
"It was a tough thing, even though I knew some fans were interested in it I also knew it wasn’t something that dramatically had a place in this movie."
There's always the chance that J.J. Abrams will address it in Episode IX. Johnson doesn't rule that out, but adds that it's not that important to Rey's story:
"Hopefully it can be addressed elsewhere or even [Episode IX director] J.J. [Abrams] may address it in the next movie. But it’s not something that’s particularly interesting to Rey, so we kind of had to follow through.”
But Snoke is particularly interesting to Kylo Ren! As much as I have liked these first two films... if Episode IX doesn't address certain things like Snoke and answers the questions that have been built up over the past two films, I'm gonna be pissed! One of the reasons that I'm so invested in this is that there's going to be the big payoff in the final chapter. At least I hope there's a big payoff that answers questions!