Dunkjoe said:
Apparently Acnologia's resolve to destroy everything ends when he "destroyed" Fairy Tail (first time) and Igneel (second time), since he goes MIA after that. Wow what a convenient recurring super-villain. Same for Zeref, making guest appearances then disappearing.
Meanwhile the weak villains show more will to destroy the entire world by many times...
When he destroyed Fairy Tail first time, he blew the freaking island up. There was nothing left. What was he supposed to do, wait there for 7 years for them to emerge? Second time as I remember even though he lost Igneel did quite a number on Acnologia, and finally bit his freaking hand off. Don't forget there were other dragons as well, as short as it may have been. I think retreat was a logical thing to do. As far as Zeref goes, he obviously has ulterior motive, some bigger plan in which Natsu is included.