Judging from the clothing and weapons used by Moku and the other green creatures, it can be inferred that they are still living as nomads. They rely on hunting and gathering for resources and have yet to discover agriculture.
Therefore, it is logical for Moku and the other green creatures to seek food outside the Bog Forest for survival. They may also be unaware of the concept of mana species and the fact that they are not the only ones living in this world.
They are simply wild and uneducated beings. Their purpose in attacking elven villages is to survive, perhaps assuming that the elf species they encountered were similar to the wild beasts in the Bog Forest. This mindset is similar to when humans first encountered the elven species.
