It’s not programmed by genetics, but how other people interact with you.

I have a similar lack of attachment to my gender for instance. That, my friend, is privilege. It means that my outward gender expression and the way I am treated for it usually match up to my inner expectations enough that I don’t experience friction. For some people, both cis and trans, gender is more important than it is to us. People have differing values and that’s what makes the world interesting.