At least so far, the commuter folding bike market is pretty small: the Census Bureau's definition of "urban" includes some areas pretty far from what a layperson calls "urban". I gather that average residences are quite a bit bigger here than many other places such that storage is less of an issue. Moreover, I think that cities with the ubiquitous rental bikes -- like DC's Capital Bikeshare -- probably compete with folding bikes. While there are not many bike shares here in the US, they are probably located in areas where folding bikes make the most sense (NYC and DC).

Anyway, I was sorry to see the Birdy disappear here.

FWIW, I have seen a few people with STRIDAs here in DC. But it's an obvious minority overall.