tl;dr: a strategic military recognition that relying exclusively on full-custom, military-spec weapon systems is unaffordable (on either a dollar or time-to-develop basis), when your competitor is a vertically-integrated Chinese civilian+military procurement system
Which is to say that instead of leveraging SV, military funding went through the primes.
The Steve Blank piece from Tuesday had a good summary: https://news.ycombinator.com/item?id=45887699
tl;dr: a strategic military recognition that relying exclusively on full-custom, military-spec weapon systems is unaffordable (on either a dollar or time-to-develop basis), when your competitor is a vertically-integrated Chinese civilian+military procurement system