On a technical level that's true. But the actual intention here is "places where you can see the sky", not places with low light pollution. Air quality is highly seasonal, and winter tends to have far clearer skies for assorted reasons. Wouldn't you be a bit upset if you booked a place way out in the country for stargazing and every rancher had just lit their fields ablaze?

That said it's probably asking quite a lot to composite that kind of data together in any meaningful way. You need a lot of domain knowledge for that.