Comments of chapter undefined of Embers Ad Infinitum

Regarding so many heartless cases in first city, I think, 1. Maybe first city is also researching the cause of heartless disease, and some kind of containment breach is occurring. 2. Some nobles/their allies have awakened power/ price that increases heartless disease in their vicinity. 3. The bigger a settlement is, the more frequently heartless disease occurs. That's why during the apocalypse, all the major metropolitan cities were completely destroyed, but the small villages were spared.