Because if you don't pay, it's easier to send you to collections. We don't "require" it, but if you refuse to give it, you can pay everything up front and just let insurance reimburse you instead of us. Essentially when you walk out of a doctors office without paying because they are waiting on insurance, they are loaning you the money until insurance pays. It's just like if you are borrowing money for anything else, they want your license and ss#.