User blog comment:IamJakuhoRaikoben/Chapter 450: Alone in all the World, Review./@comment-25111584-20150831065015/@comment-9595671-20150831154915

I agree, after seeing this chapter and what happened it seems like there's a deeper reason to why Zeref wants the Fairy Heart now. Considering his backstory... it's not hard to see why he eventually snapped.