This may be obvious to some (anyone that's read or created "captions"), but I feel the need to re-iterate the point. A photo is just a photo. It is the eye of the beholder that makes it what it is. Take two examples:
Photo 1.. A sexy woman sitting on the floor
Normal heterosexual guy: Ooh she's hot, I would so do her!
AGP: Oh god, I wish I had her body, think I could borrow it for a few hours? I could have so much fun in that body. In fact, look at the way she looks at the camera, as if to say "Holy crap! how did you change me from a guy into this gorgeous woman? Change me back!"
Normal heterosexual guy: Mmm, I'd like her to suck on my dick for a while, bet she gives good head!
AGP I wish I was her in this situation. In fact I'm imagining they just switched bodies, and he's all disoriented like "what the hell? How did I get on the other end of this cock?", and he's all digusted that he's holding onto his own cock with juices dripping down his chin.
What's my point? AGP's (for the most part from what I can see) fullfill their sexual needs through this fantasy. It is not real life, it is not something they wish to be fulltime. IDEALLY, we want this temporary, but since such magic or technology doesn't exist, this will never be fullfilled.
That may in fact be why some transition, because there is no temporary (make me a slut for 2 hours) option. It's either male with empty fantasies, or attempt to overcome the drawbacks and live as a woman fulltime.
I also think there's something to do with every man realizing that libido drops, and sexual interest drops, and then what are you left with? Some fantasy that does nothing for yourself, which in turn leaves you to exploring separating the sex from the other feelings you have inside. IE: deciding if the feeling of being a woman is what you really desired all along.