Traveling through the Immortal Lands took years, decades, and centuries at times. The regions were vast, and each area featured dangers that took time to avoid or face.
Noah's group had been in the magical beasts' domain for centuries already. They had traveled as far as the beginning of the Outer Lands in that side of the Immortal Lands, but they had to go back now.
The whole human domain stood between them and their destination. The battle mentioned by Jordan was happening on the other edge of that area, and the political situation inside it was pretty messy.
Many small and big battles had happened among the various organization during the migration. Certain forces had lost their home after the invasion, and finding new ones in wasn't easy due to how chaotic the situation was.
The lands on the opposite side of the magical beasts' domain had remained unaffected by the invasion. That had forced the migrating organizations to fly past them to find new homes.