This is a misconception, migrating birds naturally overfeed before taking their long flights [1] and a few farms actually produce natural foie gras [2]. There was also a NYT article about a farm in Spain producing natural goose foie gras by trapping migrating geese. [ref needed]
Obviously this is totally marginal compared to the size of foie gras industry.
And no need to be in the countryside to experience this. I am living in Manhattan, Upper West Side, one of the most affluent neighborhood in the richest city of the country. It is Spectrum cable or nothing. There seem to be fiber around, but it did not make it to my street (lined with small buildings so maybe not interesting enough?). Meanwhile in France where we have spent some time this year, you get fiber in the most rural and isolated areas... Go figure.
Obviously this is totally marginal compared to the size of foie gras industry.
See
[1] https://honest-food.net/wild-foie-gras-is-real/
[2] https://www.theglobeandmail.com/life/food-and-wine/food-tren...
[3] https://modcarn.com/natural-foie-gras-in-the-wild/