Whereas certain tasks in the Offerwalls module are short and not time-consuming on their own, the tasks based on games there tend to take a longer time to complete and have a time limit for their completion. Even though such tasks are higher paid, it also means more time spent in the game itself and more difficulty in completing the task.
The introduction of the Games module is meant to be a middle ground between high-paid offers that take a long time to complete and offers that take only a few minutes of your time. In the Games module, you would receive your reward for reaching a certain milestone in the task provided.