Because the longer you wait to start getting payments, the bigger the payments will be.
This gets complicated - hang in there. The government makes you wait until "full retirement age" in order to start collecting the full retirement payout that you've earned. So what's full retirement age? Good question. It used to be 65, but Congress voted in 1983 to raise it to 67 for everyone born in 1960 or later. For those workers born between 1938 and 1960, the full retirement age varies depending on your birth year. To find out yours, refer to the Social Security online retirement planner.