In my firms we did everything we could to advance women and they still left in droves. All the special privileges and groups and HR support etc. weren't enough.
I think a lot of this stems from women's own choices. We can try to pretend men and women are the same and don't generally have differing skill sets but it just isn't true. Women are generally better suited for empathetic fields and men are generally better suited to be aggressive hard chargers with a bottom line mentality. Guess which personality type generally clears more?