Why does Naphthalene turn into needle-shaped crystals by sublimation?
Every solid material has a crystal structure.  Sublimation tends to produce good crystals because the solid can grow slowly.  In bulk form naphthalene crystals are broken and compressed and so bulk solid naphthalene looks quite different.

The exact same situation applies to snowflakes.  They are flat hexagonal structures when seen individually.  Crunch them into a snowball and they lose that pretty structure.