In the case of Stan, in addition to pleasing Martin Goodman, there's the fact that he was 40 years old and didn't have anything to show for his life. He apparently wanted to be a serious novelist but he was also married and had a kid, so he needed the only paying job he had (which he got from nepotism rather than merit, let's be real).
As Mike Avila of Syfy Wire pointed out the biggest problem with Stan's credibility is his own life.
"The entirety of the Stan Lee myth stands on this unsteady foundation: That we must believe that a man who spent two decades in comics not creating a single memorable character or story, would suddenly be primarily responsible for the single greatest creative period in comics history... and who would never come close to creating anything remotely substantial ever again. How does that make sense in any reasonable way?" (
https://www.syfy.com/syfywire/stan-l...k-kirby-credit)
In the first 40 years of life, he had nothing. If Stan was such a natural and great editor and so on, how is it that in the near two decades he ran Timely/Atlas before Kirby arrived in the late-50s, Lee didn't produce or introduce any notable comic and in fact all they did was chase trends done in the industry at large. Then Kirby arrived in the late-50s and things changed. Stan Lee had a great talent for publicity and a good sense for editing when he had his hands on something valuable and popular, and he ran a good ship as EIC in the 1960s, but then his own practices drove away Kirby and Ditko and Marvel in the 1970s had a slump it fell into until Jim Shooter arrived.
The credits would only be fair if Stan Lee actually wrote full-scripts for each and every comic. Or at the very least wrote detailed plots for issues. He said "Written by Stan Lee" and he drew a salary as a freelance writer in addition to being an editor while artists only got paid for the page-rate. Later in the decade he tried and changed that, and altered that, but it was still a dodge of his responsibility and a failure to come clean.
...as for the idea that Lee believes that these characters would last, that's neither here nor there. The Roman poet Virgil believed
The Aeneid should have been burned after he died. The Emperor Augustus refused and today the poem survives and is considered a classic. That doesn't mean Augustus is the author of the poem. Nobody has that attitude. The truth is most any writer creating any work of art (a film, a novel, a play, a music album) wouldn't be fully aware that their work would succeed or have the impact it would. All they can be comfortable and happy about is putting in the best effort and ideas into their work and hope that leads to something interesting.