Yeah, don't forget that prior to the prophecy of the Demon King being reborn, several of the countries were at war with each other. They only called a truce so they could address the demon threat.
The Eld Republic (that supports mixed races and was being invaded by the Empire) and the Lufre Dragonlands both participated in the planning meeting of leaders, but opted out of providing any actual assistance. They probably only show up at all as a way to humor the other leaders and prevent further war to their lands.
The king of the Las Beastlands agreed to send fighters, though given that he's been in secret communications with the Dragonlands king while the Elesia king actually hates them, it's possible they're just playing along as well. Maybe they're using it as an opportunity to infiltrate the united forces of Elesia and Vossheil.