Why didn't Spassky take Fischer's rook ? (round 13, move 43)

I am trying to understand this game and I just do not get why Spassky does not take the rook on move 43? I am sure it is something stupid I am not noticing.

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The OP calls it second sentence. Nice.

Actually go back to move 37. Fischer moves his rook to H8 w bishop at E5, the rook can be captured. Was Fischer trying to get an exchange?

Does it take a GM to answer this question?

The white bishop is stronger than the black rook. Additionally the white passed pawn is lost after winning the exchange.

This is one of several adjourned positions talked about during this match. The simple answer is that the bishop, by guarding both a1 and d8, is stronger than all rooks.
Although the dead wood value places the rook as more valuable, this position increases the bishop's relative value.

Well what surprises me maybe is that the rook has an absolute value of 5 deadwood points and the bishops value in that position is relative and will pass when the position does.

This was one of the most amazing of all endings. Afterwards Spassky was allegedly heard to murmur: "How can you lose when your opponent's only piece has no moves at all?"