It's because the stereotype changed, like I said. The new gold standard had the average programmer be 'male, nerdy, antisocial' and that was reflected by the rise of home computing being an almost exclusively young boy thing. The stereotype shifted in the 80s to computing being an activity for men, rates of women whom were computer science majors plummeted and it hasn't quite recovered. It hasn't quite died out because people still perpetuate the stereotype that the 1960s research study created.
You can see here in the chart that women were nearing 40% of all computer science majors in the mid-80s, followed by a sharp drop-off into below 20% today [1]. There's about a 15ish year lag period for changes in hiring, perception and stereotypes to catch up as people graduate, join the work force and cycle out.
[1] https://www.npr.org/sections/money/2014/10/21/357629765/when...
