First, staying in that world with Pan Shi present meant there was no room left for him to grow, and second, according to the rules of that world, Pan Shi's interference would not only prevent him from gaining strength but would also make him weaker over time. Zhou Tian didn't want to find himself so weak one day that Pan Shi could easily kill him. In the end, after arriving in the present world, Zhou Tian had spent no short amount of time here. When his strength had increased, Zhou Tian had been single-minded in his development and had no other thoughts to spare, but now that the momentum of his development had stalled, his mind began to consider other aspects.