Board Thread:General Discussion/@comment-29855659-20170630205901/@comment-28517148-20170701095952

The use of this ability is exclusive to the character with the highest determination. - Wiki about Save. However there are no records about anyone on Surface, who could Save. Flowey in Underground was the first, Frisk second.

''Because they are made of magic, monsters’ bodies are attuned to their SOUL. If a monster doesn’t want to fight, its defenses will weaken. And the crueller the intentions of our enemies, the more their attacks will hurt us. Therefore, if a being with a powerful SOUL struck with the desire to kill... Um, let’s end the chapter here...'' - Orange book ''The humans, afraid of our power, declared war on us. They attacked suddenly, and without mercy. In the end, it could hardly be called a war. United, the humans were too powerful, and us monsters, too weak. Not a single SOUL was taken, and countless monsters were turned to dust...'' - Ancient Glyphs They just slaughtered them all without even thinking about using Save File. Most likely humans at that time did not know that such thing exists.