In 2017, a DARPA director is estimated at $76-130k per year and program managers are estimated at $90k. While DARPA does have leeway over salaries compared to the rest of the government, they still can’t offer the same compensation as large tech companies.
The people with the right qualifications could be making way more. Experienced technical PhDs even outside of software engineering can reasonably expect $170k+. The dependence of DARPA on high quality program managers mirrors the obsession with “talent” in other disciplines.
It raises the question - was this more comparable to industry averages in the 60’s? From the Bulletin of the United States Bureau of Labor Statistics - Google Books in 1960 a PhD Mathematician in industry could make ~$11000 and $8955 in government. That’s $96000 and $78000 today. So yes, the gap would appear to be much smaller.
There is a positive and a negative argument for low pay. The positive argument is that it weeds out people who are just in it for the money and treat the role as ‘just a job.’ On the other hand the negative argument is that the low pay weeds out people who have some lower bound on what they think they’re worth. I can only assume that the widening gap since the 60’s has exacerbated this latter point.
The low pay makes the question Why do people become DARPA Program managers? even more important.