Forum:Were worms

in the film, at the the beginning of the of the battle of the 5 armies the were worms are seen burrowing through the mountains to creat a route for Azogs army. But thats it ! They are not seen anymore ! Why?! Using them he could have destroyed the dwarven and elven armies in a matter of minutes! He could have burrowed into the mountain itself! He could have the battle without losing a single orc! Then why did he make this huge tactical mistake !!!!???