Question: Why didn't Chris want the cure to spread in the end?
Answer: The vampires were now everywhere, with very few humans left in their blood farms. Their food supply was dwindling and it was getting to the point that they were facing extinction by starvation. The only way to keep life going was for the vampire disease to be cured and everybody to turn back human.
Then why didn't he want it to happen?
Answer: Just like the humans, he had a fear of becoming extinct.