It has very few, it's surface is dominated by water ice.

Because europa has the same impact rate as her sister but europa is one of the smoothest planets, meaning there would be water rising and forming more ice making it look like there is no craters.

IO is an active volcanic moon, and any craters are swamped with volcanic lava.
Europa is an "ice" moon and any impact is swamped with melted water, which later refreezes.

oberth

o'day

ohm

olivier

Io is the most volcanically active moon in the solar system; its surface is constantly being renewed. Fresh layers being constantly laid down means fresh, unblemished surface constantly being renewed. Europa, on the other hand, may be covered with ice; we can't be entirely sure yet.