When, other than in comics, does any character not have an obvious expiration date? In movies, you get maybe a trilogy - six hours of the character's adventures. In novels, the same - the short story genre you may get 20 pages of a character! TV series typically run for seven seasons or less, but often only one or two seasons. In no medium other than comics does time get so stretched such that the character can be the same, basically forever. So, the idea that people cannot commit to short-run characters is a bit weak.
Though there ARE exceptions, you're right in general. But I- and the writer of that CNN piece to which I linked- are only talking about the context of the comic book market in particular. And the history is clear: heroic mantles get passed in a cycle, not in a line. The general rule in comics is that the originator of the heroic ID almost invariably winds up taking it back from whomever it was passed to, regardless of whom it was passed to.
So, when a woman or minority character takes up the ID of Iron Man, Captain America, etc., you, as a reader, know that this is temporary 99% of the time. And because it is so probably temporary! it becomes a bit of a self-fufilling prophecy that this character will not succeed. At least, not in terms of generating a significant uptick of female or minority interest in the character.
This is not to say that the gender or race swap is preferable to having a full-fledged hero of another race or gender.
But, let us be clear about something else - it isn't like Marvel doesn't have female characters, or characters of other races. Asian, Hispanic, Indian, and Asian characters all exist, and have for decades. Female characters exist, and have for decades. Depiction and use of these heroes have been imperfect, I grant you - females have been depicted as eye-candy, members of various races have been stereotyped, and so on. But, as the times have changed, so have the depictions of the heroes. And, arguably, Marvel has generally been slightly ahead of the culture curve in their use - not *far* ahead, but slightly.
Change takes time. It took a long time for Thomas Kalmaku to tell Hal Jordan to stop calling him "Pieface", but he did do so.
But personally, I always appreciated it more when minority and female characters were presented with their own identities, and allowed to fail or succeed on their own merits. I loved Luke Cage, Tyroc, Falcon, etc., and was disappointed that James Rhodes had to give up being Iron Man...then cheered when he became War Machine. (Even though it meant he was wearing the "obsolete" stuff...)
The young black woman from Louisiana who became Captain Marvel was another disappointment. I liked her backstory and the character, but she was merely renting the name. We (other minority comic book buyers I was buddies with) knew it wouldn't last. It was a sore point- why couldn't she have her own name, one more appropriate to her power suite? (Eventually, she got it.)
There is an issue, that these characters do tend to be "B-list". But Marvel's only partially in control of who is on the A-list. It is, for the most part, a popularity contest. Wolverine, for example was never supposed to be a big deal*. But, the readers loved him, so he got more and more spotlight, until he became a commercial driving force for the X-Men. Marvel is always in hot competition with others - they listen to their sales numbers, and they adapt. If they are sluggish to put such characters to the fore, it is at least in part because the audience doesn't respond to them.
I'm perfectly cool with characters being introduced and failing or succeeding. What I'm not cool with is the whole second-hand nature of so many of the more recent attempts.
It's like our heroes come from the thrift shop.
So, how much risk is the company supposed to take on moral grounds? How much are they supposed to respond to critics when the audience isn't buying?
Again, the borrowed glory issue arises.
If publishers want to make female/minority characters, I'm all for it. But why must their origins be inextricably tied to having a white male predecessor? Stereotypes or not, the ones who have always been female or minority at least have their own identity.
Sink or swim, there's an intrinsic value there.
Besides, it kind of begs the question: those female and minority characters who fail...is it because of their minority status, or a lack of compelling storylines and/or art?