Or Boston?

They are a US company, after all, who generally aims to release their innovative products and services in the US first, and the US has comparatively predictable and routine driving compared to other major countries.

Why not walk before running? Especially when this is a technology that is heavily driven by machine learning?

I agree it is unlikely to work on non-US roads for a while but I can't really blame them for starting in the easiest conditions. It doesn't have to work everywhere at the outset to be useful.

Who says it has to?