I will give you the answer in one word. Advertising. As you can see, this page has advertising all over it. And yes it is annually earning over $50,000 a year just because people like you are reading this. I get all kinds of money for people viewing my page. And if people CLICK on the AD's!! My money goes through the roof!
So what are you waiting for. The lucrative business of website management and advertising awaits you. Good Luck!