Not only has his strength been stagnant, he has tried to break the barrier of the spiritual dimension but he failed. It seems he is still too weak to break out despite reaching his limit. If he can't evolve like the great mother, then he won't be able to leave.
His other option for evolution is the fragmented Origin god that is sleeping at the center of the black hole. But it is still too dangerous to attempt to eat such an entity. He has grown stronger but the zone of no return has only grown larger. It hasn't shrunk at all. This is due to the increase in the gravitational force as time passes. That means he is still in danger of dying if he approaches the Origin god.
"I can't approach the fragmented Origin god yet. The only path for me is to try and absorb souls. But I don't want to contaminate myself." He said as he looked at the black hole with longing. "If only I could create a technique for the perfect devouring of souls."