They're entirely different in many respects but no book nor TV show is essentially endless as a MMORPG is. If I spent 12 hours a day reading a novel I'd have finished it inside 2 days, similarly for watching many TV series. Yet I could spend 12 hours a day every day playing a game and continue until ... some external factor intervenes.

Books and TV shows don't have the same "reward" mechanisms (think Skinner box) they don't really relate as an experience other than that all 3 media usually involve a narrative of some form. Games feel like you're doing something worthwhile beyond sitting and consuming media as you do for a novel or TV drama; they give an illusion of achievement [often one carefully psychologically tailored to engage and retain the user as much as possible] that compels in a way other media do not.