The problem with that theory is that the 1 a year cycle for COD games began with COD4. Yet, both CO4 and WaW had mod tools. If Activision were worried about mod tools supposedly "extending the life of the game", there would not have been mod tools for either COD4 or WaW.
Also, although we didn't have mapping tools, we had mod tools for BO1. Which, again, should not have happened if there was some supposed policy in place to not extend a games life.
In fact, this whole nonsense about some supposed policy about not extending a games life cycle is patently not true since the Master Servers would have been pulled and ended the old games as soon as the next game came out. Yet, they continue to run, and hence show that the theory doesn't hold water.
No, just like the theory that DLC competes with mod tools, this theory about Acitvision being worried about older games competing with the new games is simply not true, and doesn't stand close scrutiny.