In game 1 of the 2012 WCC between Anand and Gelfand, black ignored his passed pawn advantage. Why?

Question

In the first game of the WCC 2012 between Anand and Gelfand, which was drawn, Gelfand had a passed pawn on a6. Could he not have exchanged the major pieces and then tried to win with it?

Why was the passer ignored and the draw accepted?

[Title "Viswanathan Anand-Boris Gelfand,Anand-Gelfand World Championship Match, Moscpw Russia, 5/11/2012"]
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1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.cxd5 Nxd5 5.e4 Nxc3 6.bxc3 Bg7 7.Nf3 c5 8.Bb5+ Nc6 9.d5 Qa5 10.Rb1 a6 11.Bxc6+ bxc6 12.O-O Qxa2 13.Rb2 Qa5 14.d6 Ra7 15.Bg5 exd6 16.Qxd6 Rd7 17.Qxc6 Qc7 18.Qxc7 Rxc7 19.Bf4 Rb7 20.Rc2 O-O 21.Bd6 Re8 22.Nd2 f5 23.f3 fxe4 24.Nxe4 Bf5

Answer 1

There's a great analysis of the game here: 2012 FIDE World Chess Championship: Anand vs. Gelfand - Game 1.

According to the video, it is easy for white to get one of his rooks behind that pawn especially when both players are left with 1 rook, 1 bishop each.

Answer 2

Why? Probably because of subjective pressure of the first game of World Championship match. From what I recall when watching this game - the commentators were also surprised that Gelfand offered/agreed to a draw. His advantage was also not only in the passed pawn (which could e either a strength or a weakness) but also in having two bishops.