Why did Kepler not know about the 1639 transit of Venus?

To make this prediction, you need to know very exactly what the tilts of the orbit planes of Earth and Venus are. At the time that Kepler constructed his Rudolphine Tables that forecasted

the positions of the planets, he was not able to anticipate the 1639 transit because of slight inaccuracies in his measurements. Jerrimiah Horrocks was able to improve on Kepler's measurements and so discovered this transit.