a game can become bloated with content and it muddys the vision and core of the game… a good example would be in the new mortal kombats they added a million little side things to do and such that you just kinda got lost in.
when it comes to rebirth.. i think i could add 500 new items and 100 new enemies and bosses and it wouldnt take much away or muddy the game.. but if i added stuff like side quests, mini games and other non core game play elements.. or just made a ton more chapters that kept the game going.. it would muddy the games foundation.