Sure, I can understand that too. But, in the novels, the zombies are like a backdrop, it's a given that they are a constant danger, so they don't need to be in every scene. Other people are the real danger. Because without laws, and rules, and a strict social driven code of conduct, people turn into monsters themselves, far worse than any zombie could wish to be.
And out of curiosity, how do you guys know the budget is way less. One would think that the highest rated show on the network would actualy get a little bump to the budget.