Actually there are two reasons.

First, it is because the climate and natural environment of Yongzhou are very suitable for the growth of snakes. It is humid, has few people, dense trees, and snakes need more food, which creates the basis for many snakes.

This is caused by the natural environment.

Second, everyone knows that Liu Zongyuan's "Snake Catcher's Theory" is equivalent to putting a label on Yongzhou - many snakes.

Therefore, Yongzhou subsequently vigorously developed the snake breeding industry, resulting in more snakes.

And this is caused by humans.