A bulletin board is mostly cork, which crumbles under pressure in a way a whiteboard's hard surface never would, so the pins come out and the padding goes on before it moves an inch.
Pro tip: Take a wide photo of any seasonal or curriculum display before taking it down, since recreating a well-loved classroom bulletin board layout from memory rarely works out the same.
Watch out: Remove every pushpin, staple, and tack before handling the board; a board full of forgotten pins is a real puncture risk when carried against your body.