"Qualification"
The Old World known as Plague Focal World had maintained a strict limit on the number of "Infection Lords" since the world's birth. It was not that the world wanted to restrict powerful beings like Infection Lords—it could only withstand and contain so many of them.
However, Plague Focal World was quite special. Unlike other worlds, which were "rooted" between the planes from the moment of their birth, its coordinates had remained unchanged. It was like the trees in a forest: their roots only grew deeper with the passing years and never left their original positions.
Plague Focal World, however, was a "living world." A special mutation had produced sky-piercing tentacles called World's Foot on its surface, allowing the world to wriggle and crawl through the relatively sparse outer planes, and even "parasitize" and "infect" other worlds.
This unique trait quickly attracted the attention of the Prime Material Plane.
When the special envoy arrived in the Old World, he unexpectedly discovered the immense potential of its Sick Ones. Some had even developed to the point of rivaling true gods.
Considering Plague Focal World's infectious nature and potential danger, at the peak of its development, a joint army from the Prime Material Plane suddenly arrived. War was on the verge of breaking out.
After its various laws were sealed and the world suffered severe damage, the Sick Ones could no longer even reproduce in the most basic sense. The development of disease throughout the world came to a complete halt.
Not only were the number of qualifications forcibly reduced, but no new ones could be added either.
Only by waiting to infect a new world and using the laws of that infected world to develop anew could more qualifications possibly appear.
In short, the number of qualifications had not increased