Upvote:5
It's called the substitution effect in economics.
Eggs are fundamentally cheaper than other forms of protein such as meat or fish.
When shortages of "high end" proteins cause their prices to rise, people "trade down" to eggs.
The prices of eggs rise less in absolute terms than those of the other proteins.
But eggs rise more in percentage terms (from a much lower base). because of people "leaving" other proteins and substituting eggs.
Upvote:6
Producing eggs on a large scale requires feeding your hens grain. I deduce that the shortage of shipping space meant that priority would have been given to grain for human consumption, so the price of chicken food would rise.
Since eggs weren't rationed during WWI, but meat was, demand for eggs would rise. With production costs and demand both rising, eggs would become more expensive.
During WWII, eggs were rationed, and people were encouraged to produce their own, presumably as a result of WWI experience.