A question about immersion

The concepts of diegetic and situated immersion, which were described in last weeks a tutorial really makes you, think. How is it that one can so easily be immersed into a game and unconsciously get so evolved in a particular virtual world? Mark described that situational immersion can only be found alongside or after diegetic. However if you think about it carefully is this really the case. I know this is a point that could be argued for a very long time but I thought I should just express my personal opinion on this theory. In video games you immerse yourself into the world, which is the whole point of the game. When the immersion is broken the impact of the game becomes less and less. So the whole point of them is to involve the player as much as possible to keep them interested. Therefore the immersion becomes an advertising technique on how good the game is. The concept of diegetic immersion is where the player is embodied into the playing world. However why is it that situated immersion needs to be diegetic first. Why cant there automatically be situated. I understand the fact that you must first learn the game to for it to become second nature. Wouldn’t you say though that because of this generation’s adaptation to video games that the hardcore gamers are automatically in situated immersion? Where also the longer you have this immersion technically the better the game. Therefore doesn’t this cancel out the dietetic before the situated. I am curious as why we need both in order for the game to be good and why it can’t just be situated.