These Kingdoms were most likely angry towards the Lelai Kingdom for letting the Half-Beast people in, and they might even attack the Lelai Kingdom. As such, they had to defend against them.
Each of the three Half-Beast Kingdoms had sent 40 million soldiers, which was 120 million in total. After destroying the two Kingdoms, they had lost about 40 million soldiers and still had around 80 million soldiers.
Zhao Fu's army quickly blocked off the path of retreat for the Half-Beast armies, greatly surprising them. They had never thought that the Lelai Kingdom would be hiding such strength.
After all, this was the Grassi world, so the three Kingdoms did not dare to stay. Now that their path of retreat had been cut off, the consequences would be quite severe. As such, they immediately tried to turn and break out while leaving some soldiers behind to take control of the regions they had taken.