You'll probably find the answer you're looking for in this thread back in November, especially in the answers given by /u/Georgy_K_Zhukov, /u/takeoffdpantsnjaket, and (less directly) /u/ScallopOolong.

The simplest version of the answer is that Washington Irving was the one who pushed the myth in his bio of Columbus. But the context was also important:

1. People like Irving were motivated to reinterpret Columbus as a herald of a new age because of the Enlightenment view of the Mediaeval period as a 'Dark Age'. Before Columbus, 'Dark Age'; after Columbus, 'Enlightenment'; that required Columbus to have been a Good Thing, and that in turn required him to have discovered more than he actually did.

2. More specificually, in the 19th century after Irving: anti-Catholic sentiment. Respondents in the November thread don't address this directly. Anti-Catholic sentiment is especially important in John William Draper's 1874 book History of the conflict between religion and science, and Andrew Dickson White's 1896 book A history of the warfare of science with theology in Christendom. Both of these pushed the Columbus-versus-the-Church narrative, far more heavily than Irving had done.

(It seems striking to me that both Draper and White picked Catholicism, specifically, as the enemy of science, given that they both lived in heavily Protestant societies, and religious opposition to contemporary scientific discoveries like evolution came much more from Protestant clerics than from Catholics.)

Jeffrey Burton Russell’s 1991 book Inventing the flat earth: Columbus and modern historians is a dedicated telling of the story of how the Columbus myth came about.