After leaving his elite summons and Dani's constructs on Alfheim, Arnold made his way back to earth. However, it wasn't because he missed his home or anything. He just wanted to meet up with his family and do some other work... like having Devon figure out the mystery hidden within the Elven blood.
If the gods were interested in it so much, then there had to be a way for Arnold to harness that strength for himself. And Devon being the expert in these things, could help him do exactly just that.
In the meantime, the dungeons had started popping up once again on Earth. The industry which had been suffering a lul, was now back in full force. In Arnold's absence, the other guilds were given an opportunity to exploit the dungeons and their resources to the extreme.