The reason why they couldn't be discovered was that there were demonic beasts that had taken human form here. The most important reason was that in the beast spirit world, demonic beasts that had taken human form were not allowed to exist. Except for some great demons that had taken human form a long time ago, if anyone were to find out that there were demonic beasts that had taken human form here, then the people of the beast spirit world would usually kill them.
Of course, for those powerful greater demons who had already taken human form, if no one was able to kill them, the people of the beast spirit world would acknowledge their existence and even allow them to establish their own sects. If those greater demons liked it, they could also join a human sect, and they would receive the treatment of a Grand Supreme.
