Why does Tolkien postpone the ne ws of Smaug's death until chapter 14?

This builds tension, and shows how brave Bilbo Baggins really is. He has no idea that Smaug is dead at the time, but he still goes down into the tunnel to explore. If he knew Smaug was dead, it wouldn't be such a brave act. (Conversely, the dwarves would have shown a braver side of themselves if they'd known Smaug was dead.)