User blog comment:FairyRaven/Fairy Tail Chapter 437: Magnolia, Review and Commentary/@comment-77.194.131.252-20150525110043

I have a theory about Makarov, he suddenly changed after the battle with Tartarus, and if Mavis said him the truth about the guild, that is to say the 4 founders was trained by Zeref himself, and this was the thing which destroyed his faith in Fairy tail.

Maybe Makarov waited for some people who could rebuild FT fro scratch without this dark past, to prepare the battle with Zeref, a new Fairy tail without connections with Zeref would be more legitimate un the destruction of the black wizard