One could say that the male-dominated publishing industry was doing its own fan fictions long before amateur presses, and eventually the internet, blew up the field. Robin Hood fan fiction. Hercules fan fiction. Oog Oog Gruh fan fiction told round the place where someone would put fire once it was invented. But the field we know today as "slash" fan fiction, is one I would venture to say was created and dominated by non-male genders.
Love, romance, sex, hurt/comfort . . . the themes of slash are what were traditionally seen as the province of said non-male genders. And while testosterone has come into the picture as the sex oft got a little more intense, it's not testosterone evidenced in the way males typically seem to prefer it to be displayed.
This came to mind tonight, as I chanced upon that old video game movie Mortal Kombat, and wondered why no one had ever transported Sherlock Holmes and John H. Watson to Shang Tsung's island to battle in the tournament that would prevent the invasion of Earth. No mystery. No detection. Let's just make Sherlock and John fight people!
If the testosterone club had gotten to putting the slash in "Kirk/Spock" before those who did, it surely would have signified the sort of battle that the TV boys gave us when Spock did go into his mating frenzy, instead of any actual love-making. "Watson/Sholto" would be a Kill Bill level dual between two trained warriors. (Of course, maybe Mycroft/Mary might be more in that line.)
Since fan fiction is the black market of non-Canonical wish fulfillment, maybe such a genre would have even filled the void of fights that started, but did not get finished in the Canon. That Holmes/Roylott set of challenges was worthy of a TV wrestling promo. Sherlock Holmes/Killer Evans, had that bullet gone a slightly different direction in "Three Garridebs." Watson
And what about the "rare pairs" of fightin' slash? Wiggins/Tonga. Kitty Winter/Birdy Edwards. Sahara King/Cyanea Capillata. It's not that the Holmesian Canon doesn't contain enough fiesty characters . . . it's that they just aren't often shown in the act of their battles.
Holmes fending off street thugs with a stick. Victor Hatherly dealing with an axe-wielding maniac. Angry dog versus monkey-man. All of these things happen within the Canon, just mostly off-stage. So one could make a case that there's fighty-fiction aplenty in Watson's records, yet Holmes turns it all into more cerebral material. Not a lot of play-by-play fight scenes.
Yet romance, in all its forms, is even less frequent, so one can see why that industry has sprung up around Holmes and Watson . . . especially once they became young and good-looking after decades of being elder gentlemen (yes, yes, there can be hot elderly guys, but they aren't the primary romance market).
Of course, if manly all-fighting fan fic had sprung up at some point, it might have depended upon a younger Sherlock and John as well . . . .