Neuranium in Star Wars

During the Clone Wars, a forged metal called neuranium is, at more than a millimeter's thickness, "impervious to sensors", and standard security scans for items coming into the Republic Senate do not include any sort of gravimetric detection for determining mass-related oddities.  As a result, a neuranium statue made it into the Senate building while secretly containing a weapon.

That's from the RotS novelization.  Considering that no more than a millimeter is required, one wonders why this substance isn't used a bit more often.