Some players were confused about the ending and the revelation that the doll maker had killed the missing girl, wondering why he did it in the first place. But while the game never states it explicitly, it's explained by the parallel with the butterflies. The doll maker describes himself building good memories with them by keeping them alive for a while, then killing and pinning them up so that their beauty and those good memories never fade. In the same way, he kills the girl and mummifies her as a "doll", preserving her beauty so that she won't grow up in a world he disapproves of.
