Black does not want to play fxe4:
1. White will take back with Nd2, improving his worst placed piece.
2. With d2 vacated, white can play Bd2! then Bxb4, freeing c2 and d3 for the Queen to batter the light squares around the King.3.If black defends those light squares around his king with Nf6, we notice fxe4 has given up g4, allowing the maneuver Nh2-g4 removing the defender.