First, why is this odd? Freeing (parts of) the world from the influence of evil people is a fairly typical heroic plot line, isn't it?
Sure. The storylines seem very similar, though, where your earlier post indicated they were not.
The Hobbit involves freeing the people of the north from the influence of Smaug. LotR involves freeing Rohan from the influence of Saruman, then Gondor and (by implication) the rest of the world from the influence of Sauron, then the Shire from the influence of Saruman. A Wizard of Earthsea involves Ged freeing himself from the influence of his shadow. Then in Tombs of Atuan he frees Tenar from the influence of the Nameless Ones. Then in The Farthest Shore he frees the world from the influence of Cob.
Sure. I don't find Tolkein's works grow ever more epic, though. The return to the Shire is for much lower stakes, really. Much episodic fiction recognizes that the stakes cannot continually increase, and some tighter, more personal storylines break up the epics. They don't go from save the neighbourhood, to save the city, to save the nation, to save the world, to save the universe, growing all the way. Games tend to have a very "low power to high power" structure that the source material seldom emulates.