Why must this be so? This is your reality, but unfortunately, we have people who go through enormous lengths to change their sex. That is reality. You have to understand - it may be anatomically, neurologically and biologically more complicated than your very black-and-white understanding of the issue. It might not be quite that simple.
But I digress - my comment was on your statement about how "the majority are born straight". Which is not true at all - when we are first born we are relatively asexual, until we hit puberty. We have no sexual preference. We are raised, however, in a society where one is expected to be straight, and this leads to confusion if one grows up and realises that they are the opposite.