Frankel makes a number of good points in this article. She should probably ask Nolan himself to answer, but I don't doubt that Nolan would give an answer that would make sense (even if Frankel didn't agree with it).
Personally, my take on Batman is that it he is a superhero that has very little to do with women (and romance, and happiness). It is about darkness, and loneliness, and madness, and the Batman I know isn't happily in love etc. I actually felt there was a strong sense of Bruce wanting to give up his crusade in order to be with Rachel - I can't think of a stronger credit to a female in the movie, even if this was suggested more than seen.
I also think Batman is about subtlety. Hence, most of the story goes on in the audience minds - what is Batman thinking, what will he do, rather than seeing what is happening in the dark. As such, it is made even more compelling. I think Frankel wants this movie 'in her own image' so to speak, and there are many alternatives to choose from (camp Batman, gay batman etc). For my part, I agree with Nolan that this was the best way to show Batman as 'REAL'. And the real Batman is a lonely, brooding bachelor. Like me.