User blog comment:FairyRaven/Fairy Tail Chapter 465: 400 Years, Review and Commentary/@comment-71.222.52.171-20151208013555/@comment-7418318-20151208023519

The parents' bodies might have been too badly damaged.

Or maybe creating an Etherious takes so much time that he could only finish one before the others started to decompose and he just had no means to preserfe them available.