Designers would love to comprehend the exact causes of immersion. In a more practical world, this task would fall to those who theorize about games for a living. Oh well.
Theorists vs. Theorists
For most of the young history of videogame theory, humanities scholars have taken game immersion to be the same as the story-based variety. Publish-or-perish lecturers have written lots of journal papers that turn everything imaginable into "narrative," and so have stretched the idea beyond any possible use. You could say they're playing games of their own design.
One prominent position, known in videogame theory as "narrativism" or "narratology," asserts in its most extreme form that every game - every single one - implies a narrative. Immersion is a function of "agency" in, or interactivity with, that narrative. The 688-page textbook Rules of Play: Game Design Fundamentals, by designers Katie Salen and Eric Zimmerman, finds narratives in such games as poker and Breakout. Because this approach treats games as texts, critics can cast them in structuralist terms, and thereby increase their credibility rating with peer reviewers and conference organizers.
The main alternative approach is "ludology," which discusses immersion in terms of gameplay: Rules, interface and actions. Ludological theorists say, though games have elements in common with narratives, they are fundamentally different. Using this strategy, ludologists get cited by narrativists who try to repudiate them, and citations earn credibility points with journal referees and tenure committees.
Believe it or not, the ludological approach is relatively recent in videogame theory. Uruguayan game researcher Gonzalo Frasca popularized the term "ludology" in 1999, though it originated in board gaming in the early 1980s. Derived from ludus (Latin, "game"), "ludology" may be a back-formation from "ludography," designer Sid Sackson's term for a bibliography of game designs.
Ludologists differ from narrativists because they admit they actually play games. Nordic theorist Espen Aarseth wrote in his 2004 article, "Genre Trouble," "Among the many differences between games and stories, one of the most obvious is that of ambiguity. In Tetris, I do not stop to ponder what those bricks are really supposed to be made of. In DOOM, there is no moral dilemma resulting from the killing of probably innocent monsters. ... Adventure games seldom, if at all, contain good stories. Even the most entertaining of these games, like Warren Spector's Deus Ex (1999), contains a cliched storyline that would make a B-movie writer blush, and characters so wooden that they make The Flintstones look like Strindberg."
To ludologists like Aarseth, immersion is a function of non-narrative gameplay: "What makes such games playable at all, and indeed attractive," he wrote, "is the sequence of shifting, exotic, often fascinating settings (levels), where you explore the topography and master the virtual environment. The gameworld is its own reward, and the end, if and when it comes, does not offer dramatic satisfaction, but a feeling of limbo. There is no turning back, and no going forward. You are no longer employed by the game. Time to buy another."
Does any of this bring us closer to an understanding of immersion? These being humanities professors, no one has yet offered a testable, falsifiable hypothesis. Only a few scholars, such as Salen and Zimmerman in Rules of Play, seem interested in improving immersive game design. The rest, in thick books from university presses, on blogs like Ludology and The Ludologist, and in conference proceedings of the Digital Games Research Association (DiGRA), squabble endlessly over semantics.
In his DiGRA LevelUp 2003 paper, "Ludologists love stories, too: Notes from a debate that never took place," Frasca claimed there is actually no great gap between the two positions, and the controversy arose, among other reasons, from confused definitions of "narratology," "ludology," "narrativist" and "ludologist." Frasca's paper prompted a testy response from University of California Irvine professor Celia Pearce at DiGRA 2005. In "Theory Wars: An Argument Against Arguments in the So-called Ludology/Narratology Debate" (.DOC file), Pearce accused Frasca of "deepening the gap by further polarizing the alleged two sides.