In the past, Samael and Demos were considered rivals, the greatest guardian spirits to ever serve the creator. They were both matched in strength, intelligence, and vision but what Demos lacked which made him inferior to Samael was ambition. To take the place of the creator, the life guardian spirit shamelessly invaded the mortal world, killing thousands of its most powerful warriors and mages and ultimately using their life force to increase his own strength.
By the time the powerful warriors and mages were all gone and his strength was not yet at the level which he wished it to be, Samael pushed his attention to the normal villagers and inhabitants of the various kingdoms. Even though they had no cultivation base making their life force almost insignificant, it was a different story if a massive amount of them are slaughtered. In the end, the numbers made up for the lack of quality.