I can't speak to advertising, but finance and medicine are some of the few employment traditionally open to women: tellers and nurses. Of course, they aren't traditionally represented in the higher levels of those industries. That seems to be changing, but I suspect the "traditional field" aspect is the key-in-the-door there.
Software, and similar science, technology, and engineering industries, don't have those kinds of traditional positions, making the imbalance more obvious and less, well, fixable.
Could you tell me which part of the software industry currently has a majority of women? (We agree that "does" is present tense, right?) I seem to be missing it.
"Computer programmers used to be almost exclusively women."
True. But that was before I was born. And I'm 45.