If you’ve clicked here expecting epistemic rigor, you’ve come to the wrong place. With that disclaimer out of the way however, I had some ideas I thought I’d share:
The basic dynamic of feminine gossip is as follows:
On the one hand, sharing sensitive information with another person lets them know that you trust them and that they feel close to you and that having dirt on them is reason to think that reciprocating is mutually assured destruction rather than suicide.
On the other hand, sensitive information is generally kept secret for a reason and there are negative consequences when it gets out.
The problem is that telling secrets as a signal of closeness implies that not telling them is a signal of distance and ostracism (i.e. women say "why won't you tell me, don't you trust me?"), and so if you tell a secret to one close friend, you have to trust that this bond is stronger than the bond between them and their other close friends. When there are so many people in a group and when each individual person has any number of personal factors in their decision making, it doesn't matter if every person in the group has at least a 9/10 level of trust in every single other person in the group; 9/10 trust only means anything if having it means that they won't let things slip to third parties with whom they have 9/10 social trust.
I reckon that men have mechanisms to build trust with each other that have nothing to do with how much information they share with each other. In a male group, guys will ask each other what the reason for something is, get the response that "sorry, this was told to me in confidence”, and the one who asked will just accept it without skepticism, as the very fact that they've received such an refusal is a guarantee that their secrets will also be kept safe and that they can just think about the task at hand rather than having to constantly sort out the drama of the social group. Ironically, men demonstrate trustworthiness by keeping secrets rather than by trading mutually assured blackmail. They rely more on shared struggle for building trust, and when they keep secrets, this signals caring for the good of the group above the personal social power that comes with knowing everybody’s secrets.
In groups dedicated to some larger goal, this frees group members to just focus on the task at hand rather than having to constantly sort out the drama of the social group. It is especially important that social dynamics work this way among the group of people in charge of military secrets and such things.
I reckon that psychological masculinity also inherently comes with a degree of social retardation such that there are higher marginal returns in keeping to a blanket policy that “nothing will ever leak if I never tell anybody anything.”
The man’s dilemma:
To the masculine person, the feminine system of trust doesn't make sense and is hard to navigate. The woman asks "why won't you tell me, don't you trust me?" and the man has no idea how to respond to this attack, he's being asked to learn the entire system of feminine trust all at once and to make the right decision in its framework without having any of the background social infrastructure or background knowledge one would need to make a responsible decision. He doesn't even have the social vocabulary which is necessary to articulate the dilemma he has just been thrust into.
On the other hand, to the feminine person, the masculine system of trust is confusing too, and they feel excluded when they are asked to participate in it because they don't have as much experience building trust without sharing information. To women, the prospect of being friends with somebody for years without even learning their first name or favourite colour is mindblowing. Women see this system and regard it as ‘secretive’, ‘toxic masculinity’. Men see the feminine system and regard it as ‘dramatic’ and ‘gay’.
‘The’ Bargain Of Heterosexual Marriage:
A bargain of heterosexual marriage is that from the man, the woman gets somebody who is a complete social virgin to the drama scene, somebody who she can trust with greater certainty to keep her secrets (and who won't spread her girlfriends' secrets when she tells him), and somebody with whom she can escape the emotional labour of predicting and navigating the social minefield.
In return, the man gets somebody who better understands social dynamics and who can manage them for him, and he gets somebody who knows how to break down his walls and scratch his social itch of sharing info with somebody and being understood.
To put it another way, the men and women involved in it both get to experience a new kind of safety, one different from the type that they usually experience. The woman gets to finally experience the safety of not having to look over her shoulder so much to balance the two conflicting incentives of the social group's game of drama, and than man in turn gets to finally experience a setting where closeness is socially acceptable.
Some evidence that this speculation might make you try to seek out:
Sex differences in google search histories e.g. women searching things like "why are men so secretive" or "why won't he open up to me?" a men searching things like "why are women so dramatic?" or "why does she need to know xyz?"
Measurable sex differences in engagement with gossip
Demonstration that women care/think more about people rather than things and goals and victories
I think this post would benefit from breaking down the concept of "trustworthiness" more. If someone keeps secrets in general, then yes that makes you more able to trust them to not reveal your secrets, but it also makes you less able to trust them to not be secretly conspiring against the community.
Similarly: Blackmail is good. http://benjaminrosshoffman.com/blackmailers-are-privateers-in-the-war-on-hypocrisy/