Because you keep asking that question

 The title of the post is Joss Whedon's famous answer to why he writes strong female characters.

In recent weeks I've encountered several members in good standing of the He-Man Woman Haters Club. They all say roughly the same thing.

"Women have no business in SF/Fantasy/Horror. They don't understand it, because they're stupid and they just gloop it up with their romance."

As with so many things, the hateful seem extra empowered lately, as if they realize they are winning.
So, since romance in science fiction is a recent thing, thrown in by silly women who can't handle space ships, I guess the following never happened.

1) John Carter never courted Dejah Thoris under the light of Thuria and Cluros in the ruins of the city of Thark.

2) Antonius Block never played chess with Death over the whole of Sweden so he could see his Karin one last time before death.

3) Brunilla never found Uncle Einer sleeping under his green wings.

4) Jim Kirk never fell hard for Edith Keeler.

5) We were never introduced to group marriages, line marriages and polyamory. Because a man like Heinlein would only writer about giant bugs being blown to bits!

6) Logan made his run alone, without the romantic entanglement of Jessica. He also didn't spend two more books hunting for her across the post-apocalyptic world after the domes fell, or on an alternate earth.

7) Buttercup and Wesley, enough said. William Goldman preferred to write the emotional violence of Lion In Winter instead of True Love.

8) Dracula simply came to England to feed, not in search of his long-lost love. And he was quickly put down by clever men, who acted solely out of fear and not for love of the same lady.

If you're wondering why I left out Star Wars (me, who thinks Brian Dailey sitteth at the right hand of the Great Flanneled One), the big romance occurs in The Empire Strikes Back, much of which was written by Leigh Brackett, who died during filming. Production was shut down for her funeral. So, it's just a woman glooping things up with her romance.

Women have been writing in the genre since the beginning. We are not a new feature. Many, like Alice "James Tiptree Jr." Sheldon published under pseudonyms. More, like Andre Norton, Leigh Brackett and Julian May took advantage of androgynous names. Still more used initials, CJ Cherryh, AC Crispin, JK Rowling.

Here at Inkstained Succubus, we are proud of our women writers. We are proud of our men writers. We are proud of our trans*, gay, lesbian, bi, asexual and straight authors. And we do not require anyone to hide. The only way we won't be proud of YOU is if you send us the usual cliche-riddled stereotypes that make us wonder if you know any women, regardless of your actual sex.

For more reading on the subject of sexism in fandom and SF in general:
http://www.thegalaxyexpress.net/2013/06/out-with-old-boys-club-in-with-new.html
(this explains the dust-up that started it all)

http://seanan-mcguire.livejournal.com/513901.html 
(as does this)
http://geeksout.org/blogs/amberhardfemme/comic-con-i-love-you-youre-bringing-me-down
(A chronicle of a recent incident at ComiCon)

Seanan McGuire on being GeekCred checked at ComiCon
 http://seanan-mcguire.livejournal.com/524767.html

http://www.thegalaxyexpress.net/2013/06/more-posts-about-sexism-in-science.html

http://www.fangsforthefantasy.com/2012/10/writing-horror-while-female.html

http://www.doctornerdlove.com/2011/11/nerds-and-male-privilege/