There is a chess adage that the threat is sometimes stronger than the execution. In this game, maintaining the pin was stronger than taking the rook, 1) because it forced White to keep defending it so he would loose only the exchange instead of a whole rook, thereby 2) hindering him from mounting any counter-activities; 3) keeping the White rook on the board and immobile significantly reduced the mobility of White's other pieces, hindering him from protecting his other weak squares. The game is a fine example of boa constrictor strategy in action. VHM.
(Very high mojo.)