Eggs, the odor,the shells of various colors and sizes represent a valuable seasonal food source for many birds and mammals. They contribute to the survival and nutritional needs of those that are fortunate enough to find a nest or a single dropped egg while out on their rounds. Some most likely make a purposeful effort to find as many nests and eggs as they can when they realize it is that time of year.
Eggs I have found years ago have great attraction for all predators in various forms. Egg yolk powder is a great thickener and adds a quality ingredient to a bait or lure. Egg culture is about as good of an attractant as any we have found in testing.
Most any natural occurring potential food/prey odor will attract attention and get some interest when found. Animals know what smells familiar or looks to be something of interest. Eggs can be a subtle odor in some forms of preparation, while aging a bit and adding something can spice up its attraction and odor emission potential. This is very helpful in colder temps and desired when placed in open air conditions.
I have used egg and egg byproducts in many forms of delivery with good results and continue to do so to this day. Eggs are not a target specific product, they are a universal food opportunity for lots of animals and many will find interest if they get to it first, that is just trapping.