After all, Lampard is just one-trick pony.
His passes are mostly square passes, with the odd long ball intercepted by the other team's defence. He has no ounce of creativity to split up the opponent and create goal-scoring chances. All he knows is to run into the penalty box when the wingers have the ball and wait for the ball to land on his feet so he can shoot and score. Another note is that he's seldom injured because he rarely gets himself to put a crunching tackle on the other team's players, thus he is unsuitable for a defensive midfielder role.
The reason he's not scoring for England is because they do not have wingers that can cross the ball in for Lampard to shoot. I conclude that Lampard is an unnecessary burden in the team and deserved to be booed.
