None of the bishop trades is  particularly appealing to White. He has a more important job for this  bishop.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1c4  3... f8c5  4. c2c3  4... g8f6  5. d2d3  5... e8g8  6. e1g1  6... d7d6  7. c1g5 A  favorite line of the Armenian GM. 7... h7h6  8. g5h4  8... g7g5 The principled choice. This is what makes the Bc1-g5  maneuver somewhat risky for White. He may end up with a permanently locked bishop. 9. h4g3  9... a7a5 Stopping the queenside expansion of the white pieces. 10. f1e1  10... f8e8  11. b1d2  11... c5a7  12. d2f1  12... c8e6 