The chicken leaves a slimy coating on the egg that seals and protects it.
I've noticed in the USA that even the factory farmed organic brands taste horrible, like the chickens are living in filth. The only good brand I've found is Farmer's Hen House organic. They're like $5 US at Whole Foods :/
Unrefrigerated eggs can last a long time in a cool dry place, but if they are in a moist or warm location they will not last long at all.