Q: Why do you think the X-Men didn't find their audience until two decades after they were created? -- @godofthunder851
A: I've got a minor quibble with your timing in this question -- it was more like 12 or 15 years, really -- but you've got an interesting point there. I think most comics readers are well aware of that piece of trivia about how the X-Men were about to get the axe before Giant Size X-Men #1 breathed new life into the franchise and set them on the path of becoming what was probably the single most popular and influential franchise of the '80s and '90s, and that's not really how things usually work. In comics, you tend to either come out of the gate to massive, enduring popularity (like Batman or Spider-Man), come out strong and then fade away for whatever reason (like, sadly, Shazam!), or just sort of flounder in the midcard. It's rare that something sticks around on the edge of being canceled for a solid decade before it finds its footing, and nobody bounced back harder than Marvel's Merry Mutants.
But really, what you're asking here is two separate questions: Why didn't the X-Men take off in 1963, and why did they in 1975? So let's look at the history and see if we can't figure it out.