DC has a stronger IT job market than possibly Silicon Valley and New York. DC has been a top city for IT talent and is probably the best of the three due a significantly lower cost of living.
And while the cost of living is less than NYC and SF, it ain't exactly cheap either.
Amazon's decision to come to Crystal City makes sense to me because there are a bunch of young college grads and no competition from the other FAANG companies.
If you're a young, ambitious, programmer trying to decide where to start your career though, I'd suggest going to SF/SV, NYC, Seattle, or Boston because those places provide more options.
As far as the traffic, it's the worst in the country just about, usually fluctuates between the worst or 2nd worst.
Most major tech companies have some presence in DC and those that don't are coming here everyday it seems.
In the Bay Area, that's a heck of a deal.