Answer:
It would be too impractical to try to colonize and could lead to other conflicts.
Step-by-step explanation:
The spheres of influence were designed so that the controlling powers could trade efficiently from China. Trade was the most valuable use of occupying land in China at the time and it was under control. An attempt to colonize against such a huge country, with a high population, so far from home could be impossible or at least very costly. There had already been large losses on both sides from the Opium Wars.