Here's why:
* Evolution Line: Vulcanusmon is the Armor Evolution of Agumon, a Rookie-level Digimon. Armor Evolutions are a special type of evolution that occur when a Digimon absorbs a Digimental.
* Level: Armor Digimon are generally considered to be on a Champion level, equivalent to the "Adult" stage in the traditional Digimon evolution tree.
Therefore, while Vulcanusmon is a powerful and impressive Digimon, it is not a Mega form like WarGreymon or MetalGarurumon.