Rean's group had just arrived back from their travel to Darian's underwater palace. Naturally, they were received by Malo and company. Following that, Roan explained that the war between the Zasfins and demon beasts would finally leave its initial stages and enter the stage where high-level experts would enter. With that, the Zasfins would have little time to care about gathering more humans to be used in the Bloodline Trial Control Formations. Well, even if they did gather more of them, the formations would still take several more years to be rebuilt, so it didn't matter much overall.
That being said, Roan offered to participate in the war for everyone above fourteen years old, allowing them to work with the 10% of the Demon Beast Army that he would control. He made sure to clarify the dangers involved so that no one would change their minds later.