Why? 5's really the only one that's an option, given the story in the games. Ending it at 4 would be pointless and lackluster, ending it at any of the pre-4 games would be an insult with their constant "Umbrella is going down!" business. 5's the only one that wrapped things up enough that you COULD end it and have a concise story.
THE FIGHT WILL CONTINUE, AS LONG AS THE AMERICA INSIDE MY HEART IS STILL ALIVE