In a game of mine, the below position emerged.
[FEN "r1bqkb1r/2pp1ppp/p1p2n2/4N3/4P3/2N5/PPPP1PPP/R1BQK2R b KQkq - 0 1"]
It is Black to move. The computer suggests the move 6... Bd4, and then it suggests 7. O-O for White. Why doesn't the black bishop just take the white knight on e5?