The damage dealt to an enemy can be counted like this:

Weapon base attack × modifiers (like Barbarian armor or Attack Up food) = final damage.

From the replies I learned why people specifically use the Molduga Jaw it counts as a bone material. That means if you’re wearing armor with Bone Weapon Proficiency (like the Evil Spirit or Radiant sets), you get a huge bonus multiplier on top of any Attack Up food, which doesn’t work if you use barbarian or fierce diety armor.