From the introduction: The wizard Mavira was sick of travelling to different planes to do their grocery shopping, so they created a demiplane where people could get everything they needed. All the magical energy gave the store a life of its own and over time the different aisles became distinct biomes complete with creatures. The intelligent humanoid ones referred to themselves as “staff” and formed their own societies, while the unintelligent ones behaved like the animals they resembled.