I guess the simplest answer to this question would be:
Because the majority of people who are into guro are turned on by women more than they are turned on by men.

As a bi who enjoys boys in guro quite a lot, I have to sadly say, that's just how it is. Most people like to watch porn focused on girls rather than boys.

I wouldn't go as far as to say that general male guro it's hard to find, it's harder to find, but there's still a decent amount of it.

>>There is more male gore out there, but not male guro, yes.
That's true, looking at plain gore, there's plenty of male gore in pc games of all sorts.
>>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).
For me to enjoy guro, I always need to empathize with the victim. If I don't care about the victim, I don't care about the guro/gore either. If I can't empathize with the victim then it doesn't interest me.

One explanation why there is less guro with males, from the perspective on art, could be that the female form is perceived as more aesthetic. Females (and children) have softer shapes than males who have hard, shapes, edges and less pretty skin etc. (mostly genetic). In turn, a male makes less of a contrast in a guro scene, it is therefore a less interesting subject.
Certain forms of guro, especially like the stuff in freakshow, have a higher impact when performed on a subject like a woman or a child.
In cases of pure gore, likewise, I would say we are more used to the idea of men fighting, getting beaten up, drafted to war, etc, because it is so normalized in the perception of most people, it is a less interesting subject for sexual gore art.