Sequels generate a lot more revenue on games that are certain to sell. Final Fantasy series Grand Theft Auto series, Devil May Cry series, Guitar hero series, etc. By releasing a new installment its basically a guaranteed success because there is a fan base.
With a new project in a new series its always a gamble a hit or miss. You never know how an original game will be received. Some of the best games ever made have not had sequels made.







