I remember reading an article somewhere about the the development of the series. From what i remember is that capcom wanted each game to have a completely different storyline and not be connected to the previouse game in any way (ie no umbrella or t vitus or racoon city in the sequal) Bare in mind that this was around the start of the first games development.
Kind of like how each film in the halloween series was going to be completly unrelated to each other.
Kind of like how each film in the halloween series was going to be completly unrelated to each other.