I agree that NYC is not as transient as you'd think. Unless you're moving because it's unaffordable once you're in NYC it's hard to leave

and also you're bound to find employment there.
I think DC is the most transient place I've ever been. The nature of the work to be found in DMV area lends itself to travels. Anytime you have foreign organizations, govt and military I'm not sure how you're not moving at least a handful of times in your career.
People don't typically move unless you find a new job, for family or economics. Moving is a process and a hard thing to do once you're at a certain age unless you must.