confused about a move played by a grandmaster In this site :

https://www.365chess.com/game.php?gid=2941895

I saw a game between two chess professional players :

Efimenko, Zahar (2566) vs. Kaliuzhny, Andrey (2213)

[fen ""]
1. e4 d6 2. d4 Nf6 3. Nc3 g6 4. Be3 Bg7 5. Nf3 c6 6. h3 O-O 7. Qd2 b5 8. Bd3 Nbd7 9. O-O e5 10. dxe5 Nxe5 11. Nxe5 dxe5 12. Bc5 Re8 13. a4 Nd7 14. Be3 b4 15. Ne2 a5 16. c3 Rb8 17. cxb4 Rxb4 18. Qc2 Nf8 19. Rfd1 Ne6 20. Qxc6 Bd7 21. Qc2 Qb8 22. Bc4 Rxb2 23. Qc3 Rc8 24. Rxd7 Rxe2 25. Rad1 Bf6 26. Qd3 Rb2 27. Rxf7 Rxc4 28. Rxf6 Qe8 1-0


In move 12 , efimenko which is white played  Bc5 which I could not understand :

So I have two questions

1) why he did not play 12 . Bh6 , instead of Bc5 , to get rid of the dark square bishop on Bg7

which protects the king ? and 2) what is the reason of playing Bc5 ?

I am really confused and I do not understand . Help
We can note a few things about the position before Bc5 was played on move 12. First of all, white's dark squared bishop is both his good bishop (due to the fixed pawn on e4) and an active contributor in the position (dissuading black from playing c5 and taking more space in the center/queenside). Moreover, black's dark squared bishop is his bad bishop and is currently blocked in by the pawn on e5. There is not any foreseeable attack on the black king because the knight and light squared bishop are hemmed in by the e4 pawn (and the c6 pawn), there are no open diagonals or files on the kingside, and black has more defenders around his king than white has attackers. 

Therefore to answer your first question, Bh6 doesn't make sense in this position. Yes it weakens black's kingside dark squares, but white has no way to ever take advantage of that. You are also willingly trading a good and active bishop with a bad, blocked bishop.

As to why Bc5 was played... that one's a little bit harder. It's basically a high quality passing move assuming black plays perfectly. Bc5 forces Re8, a move that black does not want to play (moving a rook from a closed file to another closed file), so black will have to spend another move later if he wants to activate the rook. But on the other side, the bishop on c5 can be attacked by Nd7, which is arguably not a demotion of the knight. So the bishop will have to return to e3 eventually, effectively trading tempi with black. Maybe white figured that "forcing" black to play Nd7 wouldn't ultimately be useful for black.

Personally, I would be playing 12. a4 and just getting on with it, as I agree it's unclear what white truly gains from this maneuver (especially because we later see that Nf6-d7-f8-e6 is a useful maneuver for black to make).