I guess the answer is pretty simple, they didn't want to have a slice of the app that would be irrelevant for half of their customers. Of course most people won't use the dozen features of the app anyway, but they could/might regardless of their sex/age/race/ etc. Introducing a sex specific feature makes a distinction. Maybe they could have done it so you'd chose for the male or female version of the health app or something like that, not saying that doing it well was impossible but it would require focus and dedication for this particular problem. Maybe we will see it coming in the future, who knows? But it was certainly not their focus at the release!