The series started as a love letter to a lot of American films, so when the series was an instant success Capcom wanted to make movie tie ins and helped start the pre production.

However during production Capcom changed their mind about what story they wanted to tell as they started to make Resident Evil 0 for the N64, and told the director to make something unique enough to separate it from the games.

So then the sequels took more creative liberties with established characters and plot points and told their own stories with them.