So Joe Johnson is a great player. He's probably the third best shooting guard in the NBA behind only Kobe Bryant and Dwyane Wade. However, even the best players in the league have off shooting nights. The difference between Joe and many of the other stars in the league is that he doesn't get the to the free throw line.
Here are the average free throw attempts for the top 10 scorers: 10.1, 9.9, 9.8, 7.3, 9.0, 6.3, 7.3, 8.6, 7.2, and 3.5. Can you guess which one is Joe? The only other player below 7 free throws per game is the unconscionable gunner, Monta Ellis. In fact, you have to go down to the 29th highest scorer in the league, O.J. Mayo, before you find someone who averages fewer free throws per game.
If Joe averaged 7.5 free throws per game, which would put him right in the middle of the pack, that would add an average of 3.3 points per game since he's an 83.1% free throw shooter. What his low rate of free throws means, however, is that he cannot recover from a bad shooting night. If Joe is cold, his only option is to keep shooting and hope he starts making the shots. By contrast, the other players in the top 10 can put their head down and get to the free throw line.