It's political. To be fairly honest very few people care about lesbians in general. Guys are either turned on by it, or don't care as it has nothing to do with them. Women can use it as an insult, but in general don't care that much about it either if they aren't involved.
While I won't say it's never happened, I can't think of many examples outside of fantasy (oftentimes directed at men) where lesbians have attacked and raped children especially in the pre-sexual age groups.
Yet when it comes to gay men, the same cannot be said. When you hear about gay sexual assault it's inevitably involving men, and despite Lesbianism having been prevelent you'll notice that back in say ancient Greece you didn't have young girls being run down and captured as homosexual sex slaves the same way you had it going on with boys. This is incidently where the term "Greeking" comes from (though it doesn't nessicarly have a pedophille connotation).
In general it's the gay men that get the serious opposition when it comes to gay rights. Despite what the media might imply it's not all religious fantatics and such, nor misguided "homophobes" who dislike them for no reason other than being differant (actually most involved have reasons and frequently they have little to do with religion).
You whip out lesbian characters and such and most people are going to go "meh". I mean heck, 90% of the time when you have romance options in games you have guys asking if there is a lesbian option. Not to mention the mountains of hentai out there (where hetero and lesbian seriously seems to outnumber Yaoi). So basically someone brings up lesbianism, you get a little bit of noise like with Mass Effect, and not much happens. Bring in gay men, and well... it's a bigger deal and gets more attention.
Given that the purpose of such articles is specifically to garner attention, and whether anyone wants to admit it or not, the majority of anti-gay sentiment is men against gay men, you need to focus on gay men to really make a serious issue on gay rights.
Agree or disagree, I'm not going to argue it. The point is that if they ever decided to do an article on "lesbians in gaming" it would likely lead to a totally differant tone than the more directly disputed issue of gay men.
Truthfully, I'd imagine that if you ever seriously wanted to address the issue of lesbianism in gaming it would tend to get into things like how most of the lesbianism you see is intended to appeal to men more so than actual lesbians (although there can be overlap, you can oftentimes tell the target audience by the tone).
Also like with gay men, there isn't just one "type" of lesbian. While the stereotype is a somewhat pathetic pseudo-male (at least in the butch role) or women too ugly to land a guy, that's hardly the extent of it, especially when you start dealing with the artsy types. Not all lesbians are feminists either.