I want to because having a male body makes me feel miserable. The hair, the shape, the everything - it's all so disgusting to me, and I can't stand it. The same applies to a male voice: I can't stand to use it, and when I do, I cringe with every word I speak. It feels extremely uncomfortable for me to be in a male body, and to have a male voice.
Furthermore, it is uncomfortable to be perceived as male. I don't like being called, "He", or to generally be thought of and classified as male. Some of that is just at a basic, emotional level, and some of it is at a more logical realization that being male excludes me from things that I would enjoy, like having female friends that don't treat me differently.
The fact that I had a male form caused me to hate myself, which affected every aspect of my life.
So, I guess I want to transition more out of a desire to be "not-male" than to be "female", precisely. But, I will note that every change I have experienced has been welcomed, and I truly desire a body that appears female. I am distressed because of the things that I yet lack in that regard, and at what I have that shouldn't be there. I want to be female, physically speaking, and I can't say why for any reason other than the fact that I hate the masculine traits my body possesses with an undying passion. At the same time, I love the feminine traits, and want to induce more of them.
I can't really define that desire clearly. As for my mind... well, I am who I am, and I don't know if my mind is male or female. I do know that my personality is very feminine - how I speak, how I act... they, too... but anything more than that falls into the realm of "I dunno".