As an incentive for users to update the blockchain as frequently as possible, Bitcoin uses a lottery-based reward system. Many people become miners and try to be the first to add a block to the blockchain. Then, based on some probability, a winner is chosen and gets to add a block.

What is the purpose of using a lottery like this to run Bitcoin? Well, let’s imagine Crowley wants to buy a $10,000 car from Clarice. Using traditional currency, two people engaging in this transaction would probably go to a bank and have the money transferred between their bank accounts

SOURCE: https://www.coindesk.com/blockchain-lottery-miners-rewarded/