User blog comment:IamJakuhoRaikoben/Chapter 372: Breach, Review./@comment-4449950-20140222062948/@comment-24066070-20140225090054

My impression is that Kyouka merely answered Erza's question.

Why do you do these things?

Because that will lead to a world approved by Zeref.

Why blindly follow him?

We were made by him, so it's normal for us to follow his ideals.

To me, it did not seem like a desperate craving for his affection, since they likely already have it.

Bear in mind that Tartarus has been around for many years and they only recently started to move, just around the time Zeref supposedly decided to give up on mankind and spoke of wiping them out.

I think Zeref then ordered them to make their move.