NASA didn't exist until 1958, but the notion of the Round Earth was accepted by (most) educated people even before Columbus, certainly by the time of the Crusades. How were they making money from it then? Nowadays the notion of the Round Earth is being supported by the govts and scientists of every country -- there just isn't enough money to go around to bribe them all, especially when the one who breaks the silence about proving the Earth is flat will get fame and fortune.
Every suggested motive for "lying about the flatness of the earth" doesn't stand up to scrutiny. Believe me, easier ways to make money - in fact a lot of ways to make money by opening up about the Flat Earth - all kinds of new scientific and industrial efforts at exploring beyond the Edge and so forth, full employment, new discoveries, new resources, new inventions, etc.