Why did the percentage of CS bachelor's degrees going to women peak in 1984? As shown by the following graph, the percentage of bachelor's degrees going to women in the US has increased over time in almost every major, with the dramatic exception of CS, which peaked in 1984 at 37%, then fell drastically, never to rise again above 20%.



Why are the numbers for CS so different from every other field?

This is relevant to CS education for those who want to make sure that students have equal opportunity regardless of gender.

Clarification

Since some readers seem to have misunderstood my question, let me be explicit that I am not asking why fewer women than men study CS, nor do I mean to imply that people should not be free to change their own majors. I am asking why the proportion of CS bachelor's degrees in the United States going to women fell dramatically after 1984.
Obviously, there is no way to definitively know the answer to this question.  But my favorite theory has to do with the advent of the home PC, and the original marketing of computer games to boys.  The strongest support for this theory is the timing, which means that I must now give the obligatory caveat that correlation is not causation.

Basically, the theory goes like this: as the home PC started to sell, the good folks in marketing had to choose which groups they would target with their limited ad dollars.  The earliest games that came out involved balls and shooting anyway, so young boys were chosen as the target market.  And thus began a generation of young boys who logged hundreds or thousands of hours with computers, with no corresponding boost for the girls.

As this generation of children reached university age, more boys signed up for computing majors, and professors began to tailor their classes towards this majority of people who already had some background.  Girls who did come in often felt like fish out of water (and abandoned the major), leaving us where we are today.

It does not have to be so.  There are inroads being made into this problem, and I am hopeful that with the total infusion of computers into all of our lives that is going on now, the timing is right for this problem to begin to fix itself, as the experience differential has begun to level out.