When I read a work of fiction, I'm far more conscious of whether the author is a man or a woman than I am when I read a work of non-fiction.
It's not that the main character in a novel is necessarily the same sex as the author – but one always know what sex the main character is. I can think of novels, by Philip Roth and by Andrew Sean Greer for example, where one doesn't find out what race the main character is right away -- but it's hard to think of a novel where one doesn't learn immediately if the protagonist is male or female.
And isn't the way one identifies with a female protagonist created by a male author subtly different than the way one identifies with a female protagonist created by a woman author?
I learned recently, from Franco Moretti's Graphs, Maps, Trees, that there have been many shifting trends in whether more men or women novelists are getting published. Far more men than women published novels from 1750 to 1780. But women novelists were in the majority from the 1780s until 1820. Then men dominated the field again from 1820 until the mid-nineteenth century, and women from the mid-nineteenth century to the 1870s, when the male novel became ascendant again... Moretti sees these cycles as playing a crucial role in keeping the novel a vital art form.
It seems unlikely there are any such trends for nonfiction? Possibly this is because we use so more of who we really are -- delve so much deeper into our souls -- when we write fiction than when we write nonfiction?