The software industry has been growing rapidly in recent decades, and the growth has been concentrated in a few geographic areas. So employers in those areas (especially Silicon Valley, and also smaller hubs like Seattle and Boston) have to recruit a lot of their workers from other regions, as their job openings grow faster than the "organic" growth of the local worker population.

Theory: This importing of workers has negative effects on age and gender diversity, since it means a higher proportion of jobs go to people who can easily relocate for work. That includes young people (who are less likely to have kids and/or spouses) and men (who more often receive the primary or larger income in a household). I'm sure you can think of other things that are advantages or disadvantages when it comes to moving to California for a job.

There are ways to test whether this effect exists and how large it is. For example, you could compare age and gender diversity across industries. The theory predicts that age/gender imbalance is correlated with geographic concentration of employment growth for each industry. You could also see whether these imbalances are worse within industry hubs, compared to companies in the same industry outside the hubs. (Though the effect can also spread outside the hubs if it influences a culture that gets exported to the rest of the industry.)

I'll bet geographers or sociologists have published research on this subject, though I don't know enough to search for it effectively. (I found some vaguely related papers on Google Scholar, but nothing yet with data that would directly answer these questions.) There are some historical parallels of course, like gold rushes and resource extraction booms that cause new industries to grow suddenly in a particular area.