Because of his lifestyle, he hadn't managed to make much progress as a cultivator. While his mates had surged far ahead of him on the order of cultivation, and despite coming from a lineage of extraordinary cultivators and geniuses, Gu Ri remained stuck at the Divine Soldier Stage. His bloodline was supposed to be the ultimate catalyst that would bolster his skills to enable him break through to a different stage, but for some reason, he stayed stuck at that point. It truly seemed like he wouldn't move past the Divine Soldier Stage.
The theory regarding his oedipal issues (foundational childhood problems that stemmed from his lack of a father or mother) might have lent credence to his lack of motivation both as a cultivator and as a young man. But alas, the case was the exact opposite of his elder brother, the prodigy who excelled in all the arts- Gu Yue.