Can't speak for other places, but we use imperial measurements in our recipesSo most USA recipes require 1, 2, 4, or 6 eggs. Three eggs is rare. Then if you double those you get 2, 4, 8, or 12. None of those numbers are multiples of 5. Makes sense why they'd sell 12, 18, or 24 eggs in a container in the US, because that's how our recipes are written.
Commercially, they go by weight of egg yolks and whites, grams may be more common, but I've mainly seen ounces or pounds.
In countries who actually use the metric system, do your recipes reflect this? Do you have multiples of 5 eggs in the recipes and in the egg cartons, or is it all still basically 12 eggs and divisions of 12? Curious minds want to know...