As per the game narrative, the reason why the villagers and Onbu move appears to be that they both want to go away from toxins.
Yet, when Onbu and its villagers reach a perfectly safe place without toxins, they do not stay in that place.
It does not make any sense.
It would be great to add some narrative explanation or in-game events explaining why the villagers and Onbu need to get back on the move everytime.