It's really not, and this is quite obvious, but I will explain to you anyways.
The goal is stationary, the players move. Chaotically.
You have to pass where a player will be rather than where he is. This requires anticipation, and that anticipation comes from understanding what your teammate is thinking. Furthermore, a passing lane is not some whack-a-mole that just appears and you react to it. You have to anticipate the opening of a passing lane from reading the play, or even create the passing lane by feinting/moving in a way that shifts the defense. More often than not, passes are premeditated and to be a great playmaker requires a mind for the game.
A passer who relies on reflexes will never be a great playmaker.
Slaf is not a dumb player. He has a lot to learn, but he also has a lot to build on.