I suspect something related may be playing a role today, among up-and-comers trying to get published. One of the biggest factors that holds women back in a great many fields is that women get pregnant and men don’t, and most care for young children in the U.S. (and pretty much all places I’m aware of, except possibly some of Scandinavia) is provided by the mother rather than the father, so women are more likely to have their careers interrupted for several years. To some extent this is less of an issue in writing, since a writer can work at home, but I imagine it can still be an issue- even if she doesn’t work outside the home, it may be hard for a woman with kids to have enough sustained periods of undistracted time to write in peace. Fathers are more likely to work outside the home full-time, but when not at work they may also have more opportunities for quiet and solitude. The father and mother may have the same amount of work, but it’s usually easier for the father to cram all his work into a specific time of day and then have some time unmolested, whereas being the primary caregiver for kids is more likely to mean having your work stretched out in bits and pieces through the entire day. Most women do have children at some point in their lives, and so many women seeking to be writers will have an additional challenge to overcome that most men don’t.

I’ve been reading (mostly hard) science fiction for 50 years (first time I’ve had that frightening thought), and my extensive SF library is at least 95% male authors. Indeed,, all of my favorite SF authors are male: Larry Niven, Robert Heinlein, Arthur C. Clarke, Isaac Asimov, Vernor Vinge, Bova, Forward, Silverbeg, Baxter, Anderson, Pohl, ….

Why? It’s not a bias toward male writers, or any feeling that SF must be written by men. My first SF experience as a child was written by a woman, Andre Norton, and wonderfully entertaining. It started me on a lifetime of loving SF, and I read (for a while) everything that she wrote.

If anything, I have a bias for hard science fiction–technology based, not touchy-feely–and men tend to write such stories.

Perhaps, at one time, agents and editors tended to take men writers more seriously, because men tended to work as professionals, full time, while more women writers worked in their spare time. And most fiction was bought by men, especially science fiction.

Times have changed. Today, women are 70% of the readership of science fiction and fantasy. Women writers are equally as serious as men in their attempts to be professional writers. Women do write differently: more people-oriented, more fantasy, less engineering and technology oriented.

Most importantly (and as you pointed out), agents and publishers are primarily interested in profit, and if any bias exists, it is toward writers who write the kind of stories that readers buy.

Anything else would be more than irresponsible, it would be stupid.