I think it has more to do with how the male body is seen in society. It's no desired as much as the female body is. Hardly anyone values the male form, not women, not men, but for different reasons.
The female form, on the other hand, is valued by men and women - again, for different reasons.

Even some of the men on here have pointed out a reason why, "I'm not gay" and the like. That's all fine and good but what of the women? Far as I can tell, most women on here are pretty okay with, or even enjoy, looking at female guro. As one person said, for her it's in a masochistic way. I don't know about every single woman and what their sexuality is, but far as I can tell regardless of her sexuality women will look at female guro while men won't. Of course I'm only generalizing for the sake of argument here, you'll find exceptions. And I ain't saying there's anything wrong with men not wanting to look at male guro either. You like what you like and don't like what you don't like. All there is to it.

As for myself, I'm female, asexual and androromantic (or heteroromantic if you prefer). Either way, I like men and only men. Yet I'll look at female guro when the mood hits me right. I simply enjoy male guro tho. Adore it. And I'm upset that more women out there, who can art well, are not as lecherous and perverted as I am.

As for what appeals to me, I more like to see guys beaten up and raped (preferably by another male, but I'll accept a female doing it too). I wanna see them broken down not just physically but emotionally as well, crying and giving up because they can't take whatever torture they're being put through. I love it. Of course I also like gory torture as well.

That said, I find the male form beautiful. So beautiful that I want to see it bent, broken, beaten, bruised, and bloody. It's like when you see something so impossibly cute, that you wanna hug it to death. And with me it's hardly even about the penis, it's the pelvis. I've had a sick fascination with the male pelvis ever since I held a male pelvic bone (among other bones belong to a male) as a teenager. Of course I also held a female pelvic bone but it wasn't as appealing to look at.
I can't really begin to describe just what it is about men I find so beautiful, because I certainly don't find all men beautiful. Although I guess it would be more accurate to say there's a plethora of things about men I find beautiful, but not all men have all the things I consider beautiful. Like curves, I love a man with a curvy body and big badonkadonk.

I also like more peaceful things, like just dead guys who didn't die in a violent way. But rather peacefully, to where it almost looks like they're asleep. In that sense it's beautiful because he's still, there's no fun in ruining beauty like that.

Of course I don't always feel the desire to ruin beauty like that. More often I want to tell a guy I find beautiful that he should "sit there and look pretty" for me and never do anything that could hurt that pretty face of his.

But long story short, I guess I just saw way too much of the female form growing up. Saw how it was idealized, valued, and adored. It bored me. I rarely ever saw female gore tho, most violence regarding women involved cut scenes. On that note tho, even when that was the case, their deaths or the violence they suffered was treated as more important. There was usually more of a build up, it was drawn out, treated as a big deal. Male deaths or violence they suffered doesn't usually have as much build up, it's not as important, men were just treated as expendable. Which is why I like rape and torture, since it tends to be drawn out more. There is more male gore out there, but not male guro, yes. But guro is something that must be created for a niche audience who isn't looking for a story - or to empathize at all with the victim(s). In horror films and such, cliche as they can be, there is supposed to be a story and you are supposed to connect a little with the characters.

So now, who would you think horror films are more catered to? Men. People, even those not interested in guro, go to horror films to be horrified. Men get the quick and gruesome deaths for the violence factor, women get more drawn-out and implied deaths for the psychological factor. Because for whatever reason, people find female deaths more disturbing than male deaths. So men get more dehumanized in their deaths, their deaths are given more of an over the top cool factor. When men die, it's not special, it's funny, or cool, or gross yet awesome. When women die violently, on screen, it's tragic and if you think it's cool then you must hate women.

So in short, female deaths mean more, while male death is cheap.

Sorry this was so long winded, but that's what I think at least.