Ainsworth knew that the purpose of owning worlds rather than selling them to the Earth Will was to farm resources from that world.
The specialties of the Zombie Apocalypse World were the solar crystals, moon crystals, artifacts, and zombie virus that could allow biological evolution. If he were to get rid of the zombie virus, most of those resources would no longer be available.
At that point, the Zombie Apocalypse World's only value was its status as a world. After all, with such a huge property the size of a planet, Ainsworth could make a base camp in the Zombie Apocalypse World for his subordinates.
Even Ainsworth wasn't certain whether the removal of the zombie virus would retain the strangeness of the sun and moon or not. If not, then he couldn't get solar crystals and moon crystals.
No matter what, even if he could complete a side mission or hidden mission by cleansing the world of zombie virus, he'd rather not do it.
