The world fragment appeared to be fine working with two of the clones at the same time, so they increased the workload on it. After all, most systems appear to be fine until they are pushed to their limits. Legion has to know what the limit of the world fragment is, so Legion-6 is just the next step in increasing the workload on it.
Normal world fragments enhance Origin gods to the Supreme Origin god level too. The difference between normal ones and the one that Legion built is that normal ones can only work with one person.
Theirs can work with two, but they didn't stop there. They increased this number steadily so that the limit of the world fragment would be made known. Unfortunately, no matter how much they pushed or pulled, the world fragment didn't show any instability. It continued to work normally even when all eight of them were using it.