Lets break this down.
The marriage will not return under THIS regime who don't have the divine right of the King to rule for life.
Investment in the marriage is often shallowly dismissed as 'you just grew up with it'.
No.
MOST Spider-Man fans who began reading before September 1987 were also in favour of the marriage too.
It is a lie yet convenient narrative to spin that ONLY those people who grew up with Spider-Man from Sept 1987-December 2007 are invested in the marriage.
It also makes no sense considering the overwhelming majority would've come to discover those comics from adaptations that probably did not feature a married Spider-Man.
During the marriage, the only media outside of comics depicting an married Spider-Man were a few video games and less than 13 episodes of the 1994 cartoon show, plus Spider-Man Unlimited but MJ was only in the first episode.
MOST fans would've gotten in via Spider-Man and his Amazing Friends, the 1994 cartoon or the Raimi films (maybe the 2003 MTV show but that's a long shot).
Spider-Man was not only single but actively younger in all those versions, being aged between 18-22 tops, whereas Spider-Man was about 25-30 during the course of the marriage when you do the math.
And yet those readers still read and enjoyed an older married Spider-Man and the marriage itself was part of that.
In fact ULTIMATE Spider-Man fans clearly liked the marriage too considering they had to a large extent their own version of it.
Despite being a teenager, Ultimate MJ's functions within the narrative were near identical to her older married 616 counterpart's and references to the marriage were made more than once during Bendis' run, even going into Miles' book.
Why exactly did all those kids, myself included, who first got hooked onto a younger unmarried Spider-Man embracing of an older married one?
Simple: growth and character development.
That is the crack that fueled the Marvel universe from day 1. The notion that a kid in their minds could somehow headcanon that the Spider-Man of their movies and cartoons off scree/panel got older and wound up married to MJ isn't a difficult jump to make and is itself rather rewarding.
In this sense the status quo change in BND was even dumber than it was considering mass audiences were coming off a movie franchise shipping Peter and MJ and implying Aunt May knew his secret. Jum,ping from that to the JMS status quo is an easier leap for audience than the BND set up.
In fact I've seen enough newer fans who jumped on board in BND/Slott's run who LIKE Mary jane, SHIP him with Peter and would be okay if they DID get married, as evidenced by their positive reception of Renew Your Vows under Slott and later vol 2 under Conway.
People LIKE growth, so the majority are always going to be onboard with the progressive direction, in this case moving beyond a revolving door of girlfriends into something more serious and meaningful.
Think about it. MOST Spider-Man fans for the first 25 years WANTED Spider-Man to eventually wind up with somebody. Who that somebody was might've changed but few of them actively wanted Spidey to remain in a state wherein he had a revolving door of girlfriends. Shit STAN LEE didn't even want that, he had him date 3 women and intended number 3 to be the endgame. Then Gerry Conway showed up and decided he wasn't girlfriend number 2 to be the endgame. All these creators and fans who grew up on a unmarried Spider-Man WANTED to see him progress to the point where he hit the life milestone of getting married.
Just because you regress the character back to a pre-married status quo doesn't mean that attitude will not repeat itself. Those 'newer' fans who are jumping onboard and causing the married fans' numbers to 'dwindle' aren't actually fans of Spider-Man NOT being married. They just want him to undergo growth as well, just as the fanbase of pre-1987 did.
Now let's talk about those 'dwindle to nothing' numbers.
Question: Did those people who wanted a single Spider-Man 'dwindle to nothing' in Brevoort's mind?
Clearly not.
Other question: Why does Renew Your Vows even exist and served as the most successful SW tie-in if these numbers are constantly dwindling to nothing?
Last question (for now): Wouldn't it economically make more sense to KEEP those fans and then ADD to their numbers with yet more new ones?
Because it's pretty obvious that
a) People who actively want a married Spider-Man outnumber the ones who actively want an unmarried/single Spider-Man
b) There are segments of the fanbase indifferent to either camp who therefore would not be upset by having a married Spider-Man
Oh and you know you have the fact that Spider-Man's sales are egregiously LOWER now than there were in during the marriage.
And no, that isn't a 'relative' thing at all.
In the early-mid 2000s when JMS was writing ASM and people were praising his take on the marriage, Marvel and the comic book market were still picking up the pieces from the 90s crash.
The comic book market is actually BETTER now than it was back then when you really crunch the numbers. It's just not better for Marvel necessarily.
And yet part 2 of a unremarkable JMS arc in 2005 outsold an issue of Power Play, a variant cover, hyped up, crossover starring Iron Man (in a post RDJ Iron Man mvie landscape, and during a time when Stark was under BENDIS' pen) and Miles Morales as well as the Avengers and served as a de facto tie-in to ubermegahit Captain America Civil War.
So...who's numbers are dwindling here exactly?
Brevoort might be dead set on Spider-Man being abou youth and dead set on the marriage crippling the book but lets consider the source here.
Why does Brevoort's word count for anything?
Is Tom Brevoort a revered Spider-Man expert?
No.
Is Tom Brevoort a noteworthy Spider-Man writer?
No.
Is Tom Brevoort even a particularly great editor? Just on a craft level, does he have solid gold editing skills.
No.
Tom Brevoort is BAD at his current job and he was BAD at his old jobs in the 90s.
Tom brevoort is a BAD writer to the point where he will admit as much in refence to his Fantastic Force work and his most notable Spider-Man writing credit is the lambasted Funeral for an Octopus mini-series.
Tom Brevoort exists as someone who is an authority on Spider-Man merely because he seems to think he is one in spite of his statements not holding up to scrutiny (Spider-Man is not about youth, as in it is a provable fact that that is the case holy shit, how could anyone be dumb enough to actually think otherwise it's so obvious!)
So...why in God's name does Brevoort's word on Spider-Man count for anything at all?
Why on Earth should we BELIEVE him when he says the marriage crippled the book or that Spider-Man is about youth when both are provably untrue.
Then you have this whole 'Marvel is unified' BS.
Of course he's going to SAY that and of course people will agree that that is true.
But it's provably not.
Matt Fraction, peter David, DeMatteis and other creators have gone on record post-OMD in disagreeing with Brevoort's stance
Finally never say never with comic books.
Superman's marriage came back hardcore and it didn't even go away in such a hated way.
Someday Spider-Man's marriage will return