Revolutionary_Jack, what you are saying would be fine if superheroes across all mediums stayed in their current form from the Golden Age until now. But superheroes only became more accessible for an older crowd in the 70s/80s (by "accessible" I meant that storytelling became more mature, not that adults couldn't buy superhero comics). Once superhero stories get more mature, we start seeing Spider-Man and Batman's origins come up all the time.
Not that they didn't in the first place. Even back when superheroes were restricted to comics and were for a relatively younger audience, the origins still came up frequently (this is also one of the reasons why the lack of Uncle Ben references in the MCU is a problem - it doesn't come up in places it would naturally come up).
As for MCU Spider-Man, if anything that example proves why Spider-Man is partly appealing due to his origin. MCU Spider-Man has so far gotten by on novelty and the fact they have to bring in Maguire and Garfield for the next film to capitalize on the Spider-Verse trend is very telling. It arguably isn't a version that can survive for long once you take novelty out of the equation as MCU Spider-Man isn't much of a character (so far it has survived on the novelty of it being Spider-Man in the MCU and tied to event films, which you can't do anymore).
Adam West Batman is a better example, as that version did introduce Batman to a broader audience, but a lot of that had to do with it being the first major version of the character. Batman still made it big with kids through the comic medium prior to that, and I don't think his popularity was that different from Superman and Wonder Woman's when he started out. It wasn't until the Silver Age when his comics took a hit, and that's when the Adam West show saved it as an IP.