Insufficient ratio of wing lift to body weight. Plus the bird likely had little to no practice flying. Or plummeting, as this appears to have been.
If birds could think in words, one wonders what words might have been going through its little bird mind.
Was it, perhaps, grasping a coconut by its husk...
https://www.youtube.com/watch?v=YCsfHVM5x_I is the clip of “The Hitchhiker’s Guide to the Galaxy - The Whale and the Bowl of Petunias” scene.