Any good metric ceases to be meaningful once it’s actually used as a metric, because that’s when the gamification starts.

It's kinda hard to hide that you are faking it on a national scale. Way easier with GDP.

Additionally the modern trend, in many types of public lighting, is to reduce the amount of light which shines upwards in order to increase efficient and lower light pollution.

I was hesitant to mention this, but yes, it run counter to widespread initiatives to reduce light pollution