The Superboy title during the 60's had little truck with the main Superman titles. Stories that took place there had no impact on the stories in other books. Green Arrow didn't suddenly start remembering back to his trip to Smallville when a super-powered teenager took a weird interest in teaching him archery. Batman didn't reflect back on his trip to the town. Mxyzptlk didn't suddenly start going on about how he's been pestering ol' Super-Stupe since the two were kids.

Continuity wasn't the same then. It was not what fans-turned-creators would soon make it into. If you felt comfortable tying Superboy stories in with Superman ones, fine. There's your Lex Luthor origin. If not, fine. "B-But that's NOT POSSIBLE! There's only one way to read these things! Only one!" I hear the Marvelites all cry out. Well, for Marvel fans, that's true. The existence of Superboy makes it impossible for those stories not to have occurred in Superman's history as well. It's so elementary. 

But the creators of the books didn't care about such things. A Superboy story was a Superboy story and nothing else. A Justice League story was about the Justice League, and while reasonably consistent with the premises of each individual hero, they didn't all cross over and madly self-reference across editorial lines. It wasn't until the 70's when E. Nelson Bridwell began reprinting the Superboy stories as gospel origins for the characters and Eliot S! Maggin wrote stories incorporating the loss of hair in his teen years as a primary motivation for Luthor that what happened in Superboy's book mattered at all to Superman. 

Before that, Superboy stories were fun, light-hearted tales of Superman as a boy meeting this character or that. Some things like the Legion carried over to his adult life. Most did not. There was no agency in place sifting through it all to say, "This counts! This doesn't!" It was what it was; you could take it or leave it. No one writing Superman felt any obligation to painstakingly track the ever-expanding "pre-continuity" unfolding in Superboy every month and somehow "tie it all in." Such a thing would have been considered asinine. Premises were kept reasonably consistent. If you wanted to read a fun story about Lois meeting Superboy way back when and finding him insufferable, there it was. Lois herself in the Superman stories never spoke of having known him since childhood, and no one in those days would have expected her to. Superboy was an entirely different book. The Implications Game of "if this, then this" wasn't being played by the various creators and editorial offices. Fans love that stuff, tying it all together, making sense of everyone's timeline, cataloging all the various Atlantis stories and working out a way for them all to fit together. Next, we'll figure out DC's timeline for Circe and Cleopatra...!

Except there was no timeline for those things. It wasn't that they didn't care and had no respect for the readers (Marvelites everywhere: "Yes, it was!") It's that that kind of storytelling is ultimately restrictive and uninteresting (Marvelites everywhere: "No, it's not!!") If someone in Jack Schiff's office wanted to write a story about Rip Hunter meeting Cleopatra, they did not feel the need to go poring through the DC archives to find out what Cleopatra was like when Mort Weisinger's guys wrote her and how that all tied in with what happened in that Batman story where he went back in time. The author would write his own story. (Marvelites everywhere: "Gasp!" Faint! Thump!) 

Of course, the Marvel approach is to never visit Cleopatra, but instead visit Rama-Tut or the Sphinx. When those stories don't line up with each other either, they invoke parallel timelines, recursive temporal loops, and cross-continuity interference by other-dimensional beings. Of course, all of those things are inarguably wonderful. Or they're a pile of story-telling crutches, twaddle, and examples of authors playing continuity-cop that month (six months?) instead of, y'know, writing a story. I'm sure it's all been covered somewhere, but the Marvel Two-In-One story where Queen Pearla was a bad guy who mind-controlled the Thing into fighting Ant-Man didn't jibe with her portrayal in JB's micro-world saga. Dr. Strange cured Margali Szardos of her magical curse thereby removing her powers as well as Jimaine's. I don't think word ever got back to the X-Men offices. 

I'm fine with such things. When going back and fixing them becomes Job One, your story's already gone off the rails. For Bridwell, it was crucial that those Superboy stories be brought into the Superman timeline and everything be made to fit. Maggin saw possibilities in the material to humanize and redeem Luthor as a man; to have him become something more than a simple villain. But until they did so, and imposed the storytelling "reality" of a simple, light-hearted Superman-writ-small story from a different era upon the events of current Superman titles, Luthor wasn't about any of that. After fan-think crushed everything together into one, over-riding CONTINUITY, the character was made smaller, not larger, along with everything else. 

Attempts like Johns's to fix everything all over again after the time before it failed and the one before it did the same just keep destroying the landscape and scraping the remaining ashes into smaller and smaller boxes. Not everything's going to fit, people. Ever. That's not a bug. It really is a feature. Go forward. Tell new stories. Whether Luthor's hair fell out in his teen years or he shaved his head because Lois said he looked like Fred Mertz ultimately shouldn't matter if your Luthor story is a good one, so you don't have to mention either one really. 

Ah, but continuity is motivation and you can't have character without motivation and continuity is so important especially when I rewrite it so it all fits together and fans love continuity and so I will include both Luthors and they will team up to destroy everything until a third Luthor comes along with a totally different origin and he... Y'know, I thought I was kidding when I started writing this paragraph, but I'm pretty sure that literally is the plot of Roy Thomas's DC Comics Presents Annual #1. 

The screenwriters job is to tell the story in one movie, so tying things together sort of makes sense.  Comics are more like TV shows--individual episodes and stories slowly building over the years.

It's sort of storytelling-by-the-numbers.  Just tie everything together (even things that shouldn't be tied together) that others writers created as standalone concepts throughout the years and dilute the origin.

Somehow, I liked Christopher Nolan in BATMAN BEGINS tying together Ra's Al Ghul and the League of Shadows being somewhat responsible for the decay in Gotham City that led to Bruce Wayne's parents being murdered.  That's adding flavor to the original story without contradicting it.