Or! (here's an idea):
At some point when the Ancient cultures were overthrown, as a tactic of Mind Control all Otherworld dimensions, nature spirits, and elementals were deemed to be ominious manifestations leaked from the realms of Hell. Why, Cernunnos especially was demonized and twisted into the representation image of Satan in full grandeur. It's just a suggestion.
"They had to disconnect us from that which is Natural in order for us to huddle together IN FEAR: in cities, with people able TO WHIP & CONTROL in church and state. So of course they had to label the Nature Kingdom evil. Of course!"
- Tobias Lars, speaking on the subject of nature spirits and elementals