For this question I am going to refer to Why are trans-women more common than trans-men?
I said it before in a comment on the question that this question should be closed for being opinion-based, and it was deleted by someone. Since then, an answer has been given which to me is supposing that a lot of them may be gay and being trans is for economic reasons (for prostitution). This answer is therefore potentially considered on the offensive side even though it may have been written with no offense intended.
So I will say it again. This question, to me, will only result in opinion-based answers as nobody can say why there are statistically more trans-women than trans-men.
There are also non-binary trans people who are not accounted for and this question is in the same vein as asking why a homosexuality exists.
Why are others not trans? Why are non-trans people happy in their own bodies when trans people are not until their transition is complete?
You just can't answer this kind of question with objective reasoning, so what makes this question not opinion-based?
Should all other questions asking why particular groups of people are different to others be re-opened?