Openstreetmap

I think it's just the idea that people who make contributions like doing it, and so they thought moving to a new town might bring new opportunities to make osm more widely used, but then you find out someone has already done the work. It's bittersweet because you're glad the work is done but bitter you didn't get to do it yourself

Because it means there isn't anything left to do for a new mapper. Except possibly updating things when reality changes.

my guess is either disappointment from not getting to contribute to your own town's mapping, or some much more disturbing privacy implication