Here's why:
* It depends on the developers and publishers (Activision): They decide how many games they want to make in the franchise.
* Success of future games: If future "Modern Warfare" games are successful, it's more likely that more will be made.
* Changing trends in gaming: The gaming landscape is constantly evolving. New technologies and player preferences might influence the future of the franchise.
What we do know:
* There's a history: There have been several "Modern Warfare" games already, starting with the original "Call of Duty 4: Modern Warfare" in 2007.
* The name is popular: "Modern Warfare" is a recognizable and popular name in gaming, which suggests future games are possible.
Instead of trying to predict the exact number, it's better to enjoy the games that are currently available and follow the news for any announcements about future titles!