>>280874442
Back when that flashback happened, demons grew to understand people hesitate when they utter words like "mother", but it didn't actually understand why. While the series is taking place, almost 80 years after that scene occurred, they grew more efficient in manipulating people, being able to comprehend what drives humans but being unable to actually feel those things. The series does not state that demons actually feeling emotions and genuinely getting along with humans is impossible, but that the path to that evolution would take too long, cost too many lives and generally not be worth it.