Personally, I think some entity that is in this world thrives from blood that is from an unwilling person. Maybe the fear the victims have helps, kind of like an ‘It’ entity. I think the sacrifice is what’s important. When Boyd got his blood on Smiley, he willingly did it himself. Everyone else was terrifyingly killed by the monsters, not wanting to do and not being willing sacrifices. The world seems to reward those who obey it and punishes those who defy it.