User blog comment:Jho5689/Fairy Tail 337 and onwards/@comment-11232389-20130625163146/@comment-1776824-20130625190619

The Celestial Spirit World itself is in another dimension, so summoning them in Edolas isn't very impressive, as they can be summoned in Earthland, another dimension in itself. Also, the way Lucy's keys work have been likened to Anima.