For me it's because I feel like a male on the inside and I'm uncomfortable with my body and feel like I was supposed to have a male body instead
You may feel like a woman on the inside, and a woman on the outside. For them, it's when they are a male on the inside and a woman on the inside.
I feel more like a guy, and I feel like I'm lying when I dress up and act like a girl. So that's why I'd want to transition from female to male. It would just be so I can actually be myself.
I never really intended to it's just what I was perceived as really. I align well with men but I'm not really either just me myself really. I also don't have body dysmorphia
Because I'm not comfortable with my body. It's not like "oh I'm bored" or "oh I have low self esteem" I don't fit into the "cis" mould like everyone else where they have no complaints or problems with the gender they were assigned at birth. Female doesn't suit my position, though it never did from the start. I'm in transition to become who I was meant to be, but got screwed over in the womb by the shuffle of the biology deck of cards. It's hard to describe the feeling. Someone I saw described it as wearing your shoes on the wrong feet. You feel like something is wrong, but you don't know what. Then you see your shoes and realize it and when you switch them; you see how comfortable it is. That's the closest I guess you can get to describing the feeling but it's internal (most of the time physical dysphoria aside).
A lot of people say it's like being a man in a woman's body, and vice versa for mtfs, but for me honestly that's not quite it. I mean I feel more "male" than "female", but I don't feel like that really paints the most accurate picture. For me it's the sense of disconnect and dissociation from my body, like I'm assembled wrong, that makes me want to transition. It doesn't feel like my body really, it's sort of like wearing a costume all the time.
I really can see my true male self stuck inside my mind. I really feel like him except when I remember that I'm in the wrong body. Sometimes all I can do is fantasize about myself as him( me) for that moment, I really feel happy until reality comes and ruins it. I can't explain why I feel this way but I do, and it's usually hard for non-transgendered to imagine why?
I once joked to a friend that my mind is that of a teenage boy, and that's how I feel inside. There's not really a reason, it's just who I am.
The reason one would transition from female to male is that he was born in the wrong body or is uncomfortable being assigned female at birth. This causes physical and/or social dysphoria. For me it is a combination of physical and social dysphoria that makes living as female difficult.