Race establishes one of the most important things there is as a player. The environment that you are exposed to can drastically alter your course of action as you grow and decide what you want to do in life. Someone who is raised in a Buddhist household probably won’t end up with the same interests or choices as someone who grew up in a Pagan household.
While there are a plethora of races in Arcadia, these are the most appropriate for play. This adds a few more races than in the PHB and more will continue to be added.