White does not exchange the bishops. He has already seen that d3 will become a piece of dead wood.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... a7a6  4. b5a4  4... g8f6  5. e1g1  5... f6e4  6. d2d4  6... b7b5  7. a4b3  7... d7d5  8. d4e5  8... c8e6  9. c2c3  9... f8c5 Nothing up to here can be considered a huge surprise. Hikaru has only been playing e4 with White, and Caruana repeated the same Bc5 Open Spanish that he recently chose against MVL. 10. b1d2  10... e8g8  11. b3c2  11... e4f2  12. f1f2  12... c5f2  13. g1f2  13... f7f6  14. d2f1  14... f6e5  15. f2g1 All of this is well known theory, but I think Caruana fell into the same practical trap that Firouzja did against Nepo. I'm quite confident Black's position is objectively fine here, but in practice, it feels so much easier to play the White side. 15... d8d6  16. c1e3  16... e6f5  17. c2b3  17... a8d8  18. d1e1  18... c6a5  19. e1f2  19... a5b7 Both sides were still playing very fast. 20. a1e1  20... c7c5  21. f1g3  21... f5d3  22. f2d2  22... c5c4 In my opinion, this is the move that lost Caruana the game. The position is incredibly hard to understand, but I think the main point is that Black will not be able to maintain his pawn on e5. It will inevitably have to move to e4. When this happens, Black will really regret having pushed c5-c4 because he loses any hope of fighting for the dark squares, plus the light squared bishop can end up stuck on d3 and unable to fight on other relevant parts of the board. White is only a bit better still, but Black's position feels nearly impossible to play.