[redavni]

The answer is that it is not hard to get. The problem is that you are asking web developers not weather scientists.

The US provides free updated every 15 minute forecast for an absurd number of weather variables for every 3km square of the US in a nice GRIB file package. It is the gold standard on the free domain. Want a real api? Be prepared to pay real money. All Darksky did on top of this was interpolate that forecast data across time and the map.

Without an actual meteorologist on hand to guide the process, the forecast is probably going to be bad. NOAA and the weather community are just fine with the bar being high for entry. A proliferation of low effort/poor forecast web sites would just lead to them removing the realtime data from the public domain.