A pawn that has not yet reached the seventh rank gives the queen time: it pins or blocks the pawn, the attacking king approaches, and no stalemate tricks are available.
All the drawing tricks of queen versus pawn require the pawn to be on the seventh rank with the king beside it. One rank further back, the queen wins against any pawn, regardless of file, because it can simply blockade the pawn on the square in front and bring the king up at leisure.