Seirawan Opening ... Why not 16. Bxc4?

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I've been taking a look through Yasser Seirawan's King's Indian themed games and got a query about the following. Here's the Sequence:

 

Black's play of 15. ... c4 offered that Pawn to White's e2 Bishop, seemingly "for free" ... I know there's a self-serving reason for Black's move, but I can't spot Black's real intention(s).