Yue Zhong had come to America's aid, on one hand, it was for humanity's sake, and the other was to get America to whittle down at the strength of the invaders. If they wanted him to hand over the resources necessary for him to evolve, he would rather leave.
Taff's face fell, as he stood up and called out with some haste, "No, Yue Zhong. Wait! We can talk about this!"
Although the Dino-race had retreated, America was still in a precarious situation. Within the country, there were still hordes of zombies, and beyond them, the physically stronger Dino-warriors that were impervious to bullets and blades.
Since America's protector Leo had died, even with all their combined might and resources, it was not enough to stand against a Type 7 powerhouse. If Yue Zhong was to leave, then entire America would likely be torn to pieces by the Dino-race.