Facebook boasts the greatest number of users globally which has allowed it to provide the user base that it has to advertisers. The initial amount of money spent on Facebook to get results is significantly lower than the amount required to spend on traditional media channels and that has shifted how brands spend on a marketing budget. Facebook also provides the most comprehensive tool to target audience in the form of Facebook Ads Manager which allows for extremely granular control in the form of the amount of budget you want to spend, your ad placements, etc. thus businesses get a lot of value from it.