Why not use the wyrms to win?

When the Battle of the Five Armies begins, and Dáin arrives with an army of dwarfs to do battle, we see Azog has been using giant wyrms, which he refers to as "earth eaters" earlier in the film, to come up behind/beside the battlefield to flank everyone.

My question is, why didn't Azog simply use the wyrms to battle the various military forces?, or of the objective was to obtain the gold, just go straight to it. Those things were positively huge, and could have simply devoured everyone on the field quite quickly. But no, he uses them to burrow through the side area of the mountain range to push his forces through in a flank position, and then does absolutely nothing else with the wyrms the entire battle.

the-hobbit the-battle-of-the-five-armies

Best Answer

In the lore from the Middle-earth books, the were-worms were a mythical species that did not truly exist in the world, but were intended to be utilized by their society as a parallel, established by Tolkien, to dragons in ours.

That being said, the plot device from the film does not serve the story well in that it create this possible hole. However, if one were to consider Azog's reasoning, it would be that the annihilation of the denizens surrounding Erebor would seal Sauron's dominion over that territory to the south of Angmar.