[whym]

A lot of the cherry trees planted in Japan are clones, which causes synchronicity - the cherry trees in an area are grafted from a single, best tree found there, and thus bloom at the same time for the same duration, more or less. (At least that's how it's commonly understood, I don't know about the exact science into that.) That, I think, makes the blossom feel more short-lived than a non-synchronized blossom.