BECAUSE TRILOGIES are the new 90min movie. In another 40 years, each installment will encompass 5 titles jumping right past 4 because 4 is both too many and too few. It's simple math really. If you multiply the coefficient by the least common variable, the result is no one cares about the one game anymore. More fans than you will be more disappointed with the fact that a game (or movie) didn't get a sequel than those who are disappointed with how the sequel turned out. This is the world today. Live in it.