This was a category of porn that I allowed myself to get sucked into, first before I knew I was an addict, and it came back while relapsing. I've been thinking about this topic since I read it yesterday. I've come up with two possible scenarios.
1) We always talk about the dopamine rush. When one thing is no longer enough we dive into more an more extreme material. Therefore when straight porn is no longer enough, you find the next extreme. I can see this in my viewing behavior. I'd often start of with straight porn, and has I got further an further into addiction or in relapse I'd find myself branching out more, seeking shemale porn. It was the next rush.
2) This concept hit me today. I believe it rings true a little in my life, but maybe not necessarily everyone. I had patches in my life where I questioned my sexuality. I was always in the "friend zone" with girls. I went a long period without a girlfriend, and started to question myself. But it was always a struggle to admit to this possible attraction to the same sex. In my mind I was a man, I'm supposed to like women. Turning to shemale porn seemed to work as an excuse. I was able to satisfy my curiosity, but could hide behind the fact the they looked like women. They dressed like women, had long hair like women, had breasts like a women. It was a way to justify my own viewing of it. Telling myself "I'm not gay, because they look like women." But ones sexuality doesn't have to be a black and white decision
It took a lot of thinking and eventually coming to terms with my own sexuality to consider scenario two as a possibility. I think this scenario may be true for a lot of men that don't realize it, or don't want to admit to it because they too may be at a struggle with their own sexuality. And yes, I am straight, married, and have a kid on the way. Not that that matters, but we all can have a slight attraction to men, and not be "gay". Outside of admitting to addiction it may be one of the hardest situations for a man to admit to.