In Fairy Tail, why couldn't Zeref just go to Edolas?
First, I don't remind Zeref speaking about Edoras, he may have not been aware of it.

Second, in the comment section you quote the wiki : 


  "Ankhseram's "death field" is a magic spel"


But the line could have been written a long time ago when Zeref's demons and curses weren't a thing. Now in the tartaros arc we learn that the demons from the book of Zeref use curses which are not magic. Ankhseram's "death field" could also be a curse and then not be affected on Edoras.