User blog comment:FairyRaven/Fairy Tail Chapter 453: A Father's Job, Review and Commentary/@comment-49.148.179.76-20150920123126/@comment-7418318-20150920124349

Despite their short romance, Mavis never really knew Zeref and even that was over 100 years ago. For all we know Mavis death or events in the meantime might have changed Zeref from the person she barely knew, which makes it quite hard to accurately anticipate his moves.

On top of that Mavis only had the barest idea of the kind of ressources that Alvarez had available and Makarov certainly didn't say anything about an air-ship fleet.