They have had a DC office for almost 10 years, and they hire plenty of engineers for it. Still lots of disadvantages, but hiring isn't one of them.

Having worked in DC and SV I'm not sure DC engineers are cheap, especially the ones who can clear.

I have too. The ceiling for an engineers salary is much lower in DC. Also young people have a much lower salary as well. Some managers might be pretty close in compensation though.

We are talking about DMV. Working in the city is very uncommon for big primes. All their HQs are in Tysons

It's more than DC though. Big primes have satellite offices everywhere.

I have noticed that about DC. I've met plenty of quality engineers but the salaries seem surprisingly low here. It would almost be better to take a slight pay cut but live in Richmond, VA where the cost-of-living is much lower.

Either way I have major doubts about having an engineering career in DC.

Like most of the US, DC is not an engineering or manufacturing culture as much as a sales culture. Politics and customer-facing roles are valued much more than engineering typically. What's the evidence for this? Most technology companies don't have engineering-centric offices here, they have federal and commercial sales offices - literally entire offices of nothing but sales teams with an occasional visit by a sales engineer. If the engineers aren't in the Bay Area, then they're typically associated with New York finance connections. Barring that, you're looking at even defense contractors that source to lower cost of living engineers in the South / Southeast while the majority of the revenue goes to pay for the lavish lifestyles of the already-rich and well-connected in the DC metro area.

It creates culture and political problems.

When I worked for a .gov, the amount of political blowback from a consultant billing $600/hr and workforce resentment at a consultant making $500k made the untenable.