I still don't understand how an e-book, which can infinitely be replicated at no cost to anyone, can cost $10. How on earth does this make sense? I purchased

I still don't understand how an e-book, which can infinitely be replicated at no cost to anyone, can cost $10. How on earth does this make sense? I purchased A People's History of The United States a few years ago, and now I can buy it for my Kindle for $10? Who does this? Occasionally Amazon will offer the Kindle price higher than the used physical copy price.