The wolf beasts had a very simple way of thinking. Why should the Snake King Snakel have his own territory while their much revered Wolf King didn't?
But they overlooked one very important detail, and that was Snakel had no partner.
And when Snakel first went to the Snake King valley, it was still not the Snake King valley then. It was just that Snakel had wandered aimlessly across the world for hundreds of years, and was really very tired by the time he arrived there. Plus the weather conditions there were just right. In Snakel's view, anywhere in the Beast World was the same—and so, too lazy to move on, he had just settled down there.
Thereafter, snake beasts were attracted by the Beast King and slowly gathered there to form the so-called Snake King valley.