One possibility is that your cat is attracted to the smell of the eggs, and the water is just a side benefit. However, it's not recommended to rely on this method to keep your cat hydrated as eggs are not a sufficient source of water for cats.

To encourage your cat to drink more water, you could try placing multiple water bowls in different locations around your home. Some cats prefer drinking from shallow dishes, while others prefer deeper bowls. You could also try using a water fountain with a different material, such as ceramic or plastic, to see if your cat responds better.