One shouldn't blame Ji Hao for being greedy. The axe belonged to Saint Pan Gu, and must be taken back.
Pan Heng had been in a deep sleep for long years. Even though Pan Heng world was way less powerful than Pan Gu world, after all, he was a 'saint' who created a world. As the saying went, 'a lean camel is always bigger than a horse'. To kill Pan Heng for good, undoubtedly, Ji Hao would need to take a huge risk.
If it weren't for that axe, Ji Hao wouldn't even want to talk to Green Ginseng!
No matter how much Green Ginseng and his friends could offer, that wouldn't be more important than Ji Hao's own life, would it? Ji Hao was quite satisfied with his current power. The Pan Gu bell for defense, the Pan Gu sword for offense, bringing out the best in each other, with the golden bridge for his protection. By now, Ji Hao had no excessive demands for any other treasure.