Because, IIRC (it has been a while since I’ve looked at the code) it grabs weather from the US National Weather Service… which is also a primary source of data for the original WeatherStar.

It’s useful for this purpose because all of the data is in the same format as the original down to the different forecast types and phrasing used

Were the real things ever available outside of America?

Either way, thanks to the wonders of open source here's a fork that works for other parts of the world: https://mwood77.github.io/ws4kp-international/