Why do people say that the Bayonet attack (early b4) is so strong
against King's Indian Defense:

1. d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 0-0 6.Be2 e5 7.0-0 Nc6 8.d5
Ne7 9.b4

White is just attacking on the queenside and all he is getting is
material. But Black is counterattacking on the kingside and aiming at
the white's king's throat!!!

So why is it so hard for black to play against this line?