Now Marvel, Marvel is different. Marvel deliberately resisted reboots for a long time, because the single universe was their schtick, they didn’t have a lot of success in other mediums to dilute the characters, and they weren’t beholden to older characters.
(small correction: I just remembered Marvel was called “Timely Comics” during the war years, then changed it’s name to Atlas.)
After the war “Captain America, Commie Smasher” made a go of it, but eventually yhe Timely-age superhero characters were largely forgotten. Now as Atlas comics, they mostly focused on romance comics. The silver age of comics kicked off in earnest when Marvel released the first issue of Fantastic Four. That book even recycled the character concept of the Human Torch – the original being a Nazi-fighting robot on fire, while the new one is just some guy who can catch fire – totally without any reference to the original character. The wartime characters started to slowly roll back in starting with Cap in Avengers #4 (frozen in ice during WWII, completely ignoring the Commie Smasher era).
But as Marvel rolled on, it kept continuity (or retro-actively established a continuity, a “retcon”). They explained the Commie Smasher years (that was some other guy… he’s crazy now), the made a game of letting readers “explain” little art or story inconsistencies in the letter pages (“Good job! You win an official No-Prize!”). They gave histories to characters that disappeared and came back years later. As I said, it was their schtick.
But that wears on. When DC just said “let’s forget the past on Earth Two” (with an option to keep doing that in the future), Marvel was left explaining as necessary how Cap was still alive (frozen in ice) or Nick Fury still an active spy (stolen Nazi anti-aging serum). Marvel still invented other universes for different reasons… time travel stories, visits to the [strike]Justice League[/strike] Squadron Supreme, etc… but they always insisted most comics took place in the same, major universe. Eventually they said that time itself was stretching.
I could write a slightly outdated thesis about time stretching, the multiverse, cosmic abstract entities, and the Marvel universe, but suffice it to say that they – in their goofy, comic-booky way – took great pains to give a pretense of consistency without reboots.
And eventually, that too breaks down. Because readers got every bit as worn out as you probably got reading this. So Spider-Man passes his mantle to a clone (didn’t last, story is longer now), and Cap passes his to U.S.Agent (didn’t last, character roster is longer now), and so on.
Eventually, even Marvel had to admit that its readership was limited by the sheer weight of ridiculous “maybe it will matter later, maybe it won’t” history its characters had. So it rebooted five flagship titles, basically the Fantastic Four + Avengers. It bombed, they went back.
They later created a comics line specifically as a place for new readers to jump on (Ultimate Spider-Man, the Ultimates, etc.), that was in a separate, unrelated universe. That did well. New readers on some comics, older readers happy in ridiculous-history verse…
And then the movies come along. Which is a much bigger, better business. But those end up syncing up with the much more streamlined and accessible Ultimate line than anything else. At this point, the comics are an atavistic business. The characters and old stories have value – on merchandise, as nostalgia, as source material for the movies – but not the new stories. So Marvel finally hit a big ol’ reset button. Will it last? Probably not.