After White's 22. Bc1, it seems like responding with Rd2 would keep the game alive for Black. I assume Friedel's a more insightful player than I am. What am I missing? That is, from an experienced player's viewpoint, why do we assume that staying alive with Rd2 is not worth the effort, and how would White be sure to win regardless?

[fen ""]
[White "Nakamura"]
[Black "Friedel"]
[Event "US Championship 2009"]

1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 d5 5. ed5 Na5 6. Bb5 c6 7. dc6 bc6 8. Bd3 Be7 9. Nc3 O-O 10. O-O Rb8 11. h3 c5 12. b3 Rb4 13. Re1 Bb7 14. Ba3 Rf4 15. g3 Rd4 16. Nf3 Rd3 17. cd3 Qd3 18. Ne5 Qf5 19. g4 Qf4 20. d4 Rd8 21. Qe2 Rd4 22. Bc1