It may be because their hearts are biologically unable to bear the stress, or maybe something more different is in effect......when it includes both limited humans and eternal fairies......she will always be the one to outlive her family......which may be why fairies are eternally pure and innocent......it can never be like a human family.We still don't know why it happens.To be a real family...like she did.In the end...One day, the little girls who have lost their families just vanish.Much is still unknown about fairy biology...Perhaps they wander off somewhere......come to be able to live with humans.However...You see, fairies are made so they completely forget any tough or unpleasant events, or any memories connected with them....no matter how real the family might seem......having forgotten everything...Twitch...And then, one day, they just...appear again...