The article hardly dives into the why. There could be many more reasons, for instance just the fact of being more grouped together then villagers next to them.

The article hardly dives into the why. There could be many more reasons, for instance just the fact of being more grouped together then villagers next to them. Even though they had better sanitization they didn't have access to modern cleaning technology and also not the awareness of it's importance. A shithole might be more sanitary than a group toilet if less are using it.