Star Wars essentially started out as a licensed property that was clearly being directed by one creator, George Lucas. While there was an Expanded Universe right from the start (Splinter of the Mind's Eye, the Han Solo Trilogy, the Marvel comics, etc.), whenever information from those books was overwritten, it didn't seem to cause the same level of consternation that something similar would cause now.
Yes, I realize we didn't have the internet back then, bear with me.
I think part of the issue is that we viewed things that Lucas wasn't directly involved with back then the same way we might view a movie tie in video game today. If Rhino shows up in a video game for the Amazing Spider-Man movie, and he's completely different when he shows up in the movies than he was in the video game, it's not a big shock. We know the people working on the movies have their own plans, and the video game is just a video game, and it's fun for a while, but it's not the next movie, and we all know it.
But something different happened with Star Wars. So many people loved the story. The universe was similar to Tolkien's, in that we knew there was more to the setting than what was directly pertinent to the stories at hand. But after Return of the Jedi came out, George Lucas essentially walked away from the series.
George has given tons of contradictory interviews on how many movies he intended to make and when, and Googling anything about George and what he said about Star Wars yields a massive wall of potentially contradictory information, much like George's scripts (sorry, couldn't help it). So, while I'm more than willing to entertain any issues that may come up with how I characterize things, I'm going to go from memory here, and I don't think I'm wrong. Essentially, George had said, after Return of the Jedi, that he was done with Star Wars.
What that means is that when he gave West End Games permission to play with his toys, and then Bantam Books and Dark Horse Comics, and told them they all had to play nice with one another it essentially turned Star Wars from the licensed vision of one man to a shared universe that was being coordinated by Lucas Licensing.
The thing that might be difficult for people that only watch the movies to fully grasp about people that got invested in the novels and comics and roleplaying games is that Lucas, at one point in time, was pretty clear about never doing another Star Wars movie. So if you were the type of person that loved Star Wars and were likely to follow roleplaying games, novels, and/or comics, you essentially had the "go signal" to know that this was Star Wars from this point on. All of these efforts were suppose to be set in the same Star Wars universe, and nothing else was coming out from Lucas. This was the sum total of all Star Wars from this point on, and there wasn't much ambiguity from George Lucas.
George did reserve the Clone Wars era and the time leading up to Episode IV as a "no man's land" where nobody could tell stories, but despite this restriction, George never said he was going to detail that information. It could very well be his eccentric sentimentality that reserved that era. Since he, at one time, had said he was going to do three (or was it six) other movies, he probably just didn't want to see anyone else touch that era and ruin the image he had in his mind. Cool. We got Tales of the Jedi and the New Republic era, and its all cool.
My main point with this post was just to show how Star Wars went from not being a shared world setting to essentially being a shared world setting, and then got reclaimed as "not" a shared world setting. But there is one more point I can't help but make. When George did tell everyone "hands off" about the Clone Wars and the Dark Times (as they would be known eventually), it seemed pretty clear that he didn't want anyone to contradict what he had in mind for these eras. This also implied that nothing he had in mind would have snarled the stories in eras that were given the big green light, i.e. the Knights of the Old Republic era or the New Republic era.
George never claimed to read everything that was published, but it's clear that he knew Luke was married, and that there was a comic book series detailing a Sith order that had thousands and thousands of members. Why bother putting anything off limits if you are still going to allow authors to tread on territory that you were planning on walking yourself? It's a mystery, but it's clear that despite George's very clear indication that he was done with Star Wars after Return of the Jedi, he never fully understood the scope of the shared universe he tacitly endorsed with both his permission and restrictions.