The other thing is that a number years pass in between the two games, so they could expand on that story in Season 2 while introducing those other characters more. It's would be problematic for them to jump right into all of that. But they have a lot of time to plan and Craig Mazin knows what he's doing. I like this quote from Mazin, which I think explains too why they made Season 1 so tight, covering a lot of ground. “I don’t have any interest in a spinning-plates-go-on-forever show. When it becomes a perpetual motion machine, it just can’t help but get kind of stupid. Endings mean everything to me.” He basically described the Walking Dead there.