If the cultivators from the Immortal Alliance organization launched a large-scale attack, these Devil Sects would hide in the domain of their Demon Gate Sacred Land.
It's not like the cultivators could always be here, right?
The spiritual qi here isn't particularly abundant, most medicinal herbs aren't suitable for cultivators, and it's close to the Demon Gate Sacred Land, so the Immortal Sects weren't willing to come here.
The cultivators had no better solution than to strictly guard against these Demon Cultivators, preventing them from infiltrating their respective sect's territories.
Moreover, these Devil Sects rarely venture into other domains, so in a sense, they know their place, which has allowed them to persist all this time.
Of course, every few years, some Devil Sects would be wiped out by a powerful individual.