I am going to guess what happened during these 8 years:
Timeline:
company begins working on this game.
4 years into the game dev, drastic changes occurred essentially wasting those 4 years of development.
development restarts but someone wants to increase the vision of the project to compensate for the 4 wasted years so the game looks like 8 years of solid development.
we get a game that requires 8 years of development but development only was 4 years.
welcome to real world software development 101.