As far as the government is concerned, I can't really speak on that, but I know that in the States, they have somewhere between five and 15 local coordinators per state. For example, Massachusetts is a relatively small state, but there are six local coordinators just for that state.
As well, I've been told by my colleagues in Colorado that the American population is very weather obsessed. The general population already has a different viewpoint on weather and reporting on weather, which can create some differences in the number of people willing to sign up and report.
However, I truly think it's the lack of coordinators across the country that has limited our expansion.