I’m sure many Star Wars fans were devastated when Disney bought the rights to Star Wars and declared everything except the six movies (now seven), Clone Wars (the animated show, not the anime-esque miniseries), and Rebels to be “non-canon.” Many wept for the loss of the Thrawn trilogy, the Yuuzhan Vong War, and the Jedi Knight video games, especially since they were discarded in favor of Jar Jar Binks, the Cartoon Network show, and four words that send many into a blinding rage: I don’t like sand.
Personally, I was a bit ticked with the discrediting of Republic Commando (one of their video games) and all the time that was poured into these stories and these characters—from which Lucasfilm made a fair sum of money, mind you. But, with the new movie out and the references to my favorite “Legends” media popping up in “canon” media showing up, I have less and less against the “locking of the canon.”
Much like translation and anime, the canon of Star Wars correlates with a far more important canon: the canon of Scripture. We can learn from both canons that, without a locked canon, anything could be accepted as a part of the story. It’s better for preserving that which is sacred.
The reason that the Bible’s canon was locked fairly early during an event called the Council of Hippo in 393 A.D., though it was finished nearly three-hundred years earlier, and most if not all of the Old Testament was tied down before that. From that Council, I can only imagine, came a completed copy of the Biblical canon (plus Apocrypha) and a wastebasket or two of heretical texts, thereby cementing what is true and what is false.
Lucasfilm did something similar to pave the way for The Force Awakens. They took stock of what they had for story and looked at what they needed and what they didn’t need. They were left with six films and two TV shows. However, theirs was a more pragmatic approach. Star Wars was a movie-based franchise before it was book- or video game-based. In the establishment of the canon, then, the movies and TV shows would have higher priority.
A lot of fandoms have locked canons. Lord of the Rings has its own canon. The Marvel Cinematic Universe is its own locked canon, separate from the comic books. DC creates new ones on a shockingly regular basis. I think that by 2012, Star Wars even had a few stray canons of its own. And I like to think that arguments can be made for some of the “Legends” sources. Nevertheless, it’s for the best that Star Wars locked it’s canon.