Having been personally involved with investigations in two of the examples you named, I'd say based on that and other experience that you're probably right, up to a point. But too, the habits and inclinations of homosexuals for engaging in impulsive risk behaviour and a mindset that ignores social attitudes as to norms and aberrance constitutes a handicap for their chances of long-term success. I'd bet that a larger proportion of homosexuals are both undeterred by legalities or moral strictures against killing, but they're probably caught in larger numbers as well.
The quiet guy who kills those unknown to him and usually in a location where he's transient or unknown has all the chances in his favour for continued success, whatever his sexual inclination may be. And the women who engage in such activities almost always manage to slip between the cracks of investigations, so long as they keep their mouths shut.
I had NO idea about any of this....