User blog comment:Axlorg89/Fairy Tail Filler Arc Incoming/@comment-25236004-20140922092529/@comment-7418318-20140922094446

Because now is the far better time than between the Sun Village and Tartarus arcs.

Would you really want to get all the little hints and set-ups for the Tartarus arc and then be left hanging for an entire arc in between? And then because it's been such a long time, it'll necessitate a boring-ass "what happened before we added the filler" summary episode...

Just watch the Bleach anime to see how freakin' annoying that can get. Much better to have the filler now and then have the Sun Village transition smoothly into the Tartarus arc directly.