This is wrong on so many levels. Where are you getting your data that CS is almost uniquely imbalanced?
Sweden has a complete record for what every citizen here work, their education and their gender. The data is gathered as part of tax collection and as a matter of policy they also make this information public so anyone can see what the gender distribution is for any industry or profession. 70%/30% distribution is extremely average, and the wast majority of the working population (equal amount women and men) work in such professions.
If you want the most uniquely imbalanced fields, look at the professions and industries that has over 99% of a single gender. From a few years back, that covers around 5 different professions. If the the professions from the CS field is stuck in the 1960, what should we call the psychology profession with 90% women and 10% men? Nearer the 99% bracket we have professions such as mechanics, midwifes and tile installers. If we again take a look around 90% we see professions such as veterinarians, dentists, construction worker, kindergarten teachers, secretary, truck driver, and the list just goes on and on if we were to list every profession with worse gender distribution that those from CS.
93% of the working population work in a industry that the government classified as having imbalanced gender distribution, ie professions that has above 60% of a single gender. 93% is a very huge number and without a question the norm. A fair distribution is the exception, one which hopefully will grow but where the trend has been in the opposite direction since 1960~1970 and just hopefully have now reached the peak.
The only uniqueness about CS+Mathematics as academic fields is that they have more men and women rather than the opposite.