Because Nd2 and white is big trouble. Black wins the pawn on d3, effectively placing his rook in the attack. Queen can't protect the pawn, because it will force a checkmate after the move Qf1+ followed by Nf3#
Why white queen not took the pawn on e4 ?
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http://www.chess.com/echess/game?id=80021802
In this game between on 47th move black moved pawn to the e4. Why white queen not took black pawn on e4?