Well each new sequel normally has an all new race added to it for story purposes. Most often they are central figures for the main story or at least have some major aspect behind the plot. Wind Waker gave us the Rito and Koroks who were important to the overall story for characters that can more easily travel around the great sea without a boat so Link can meet up with the more often. PH brought in the cobble who built most of the old monuments and crafted the sword Link used to stop Bellum. Spirit Tracks introduced the Lokomo who were important to the story as the ones who originally sealed Malladus and were helping Link on his quest. MC introduced the Picori who were central to the story as the main villain, and the main helper were both Picori. TP brought in the Twili again as the main race of the main antagonist and the sidekick. They were also central to the story of the game.
There is always at least one new race invented for every new game in the series. Even FSA gave us the Zuna who were the builders of the pyramid. Beyond the main story aspect of the new races there is at least one other side race added to most of the new games that might not be central to the story but are the people of some extreme region. Be that weather, sky, mountain, fire, ice, etc. But we have gotten people like the Anouki for icy regions, Zuna for deserts, Parella for water, Kikwi for forests, Oocca for the sky, etc. There is a lot of overlap with there not being a couple races for each geographical region but it is clear that the developers like to make up new ones all the time.
