It is just a matter of choice. If companies make it a priority they can do it.
I don't think companies should ever hire someone based on anything other than their qualifications for the job so of course the actual distribution should vary from company to company but if it is 60:40 m/f at one company then it should be 40:60 m/f at another (SHOCKING CRAZY IDEA) and the average should come out somewhere near the middle..