Checkmate in the opening

This game is from the French Defence, Winawer variation. Lundquist - Phillips [C15] Wien, 1980.
1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.Bd2 dxe4 5.Qg4 Nf6 6.Qxg7 Rg8 7.Qh6 Qxd4 8.0-0-0 Ng4 9.Qh4....

In the game, Black takes the pawn on f2 with Qxf2??. This is a terrible blunder. WHY?

Answer: highlight in between bracket [Black abandons the critical defence of checkmate attack. After 9....Qxf2 10.Qd8+ 11.Kxd8 Bg5+ 12.Ke8 Rd8++ 1-0]