The answers above are not very accurate.
The exchanges have 2 main sources of income. The first is a commission for trading. And the second is the payment for the coin's listing. Small exchanges take a new coin just like that, even if it's not just a very trustworthy project. Larger exchanges examine the coin more thoroughly, sometimes can even ask for a symbolic amount for the listing. But such exchanges as Binance - with billions in trading volume, do not simply take a coin. It costs a very large sum of money and small projects. Today, placing a coin on Binance is worth $ 1.5 million.
I hope now you understand where resources come from?