That has been my biggest complaint with the show, the lack of development for the post-Apocalypse world. I understand that the show just follows this small group of people, but I still wouldn't mind getting at least some idea what is going in the wider world. How many people survived? Is there still any kind of government? Military? How wide spread was the infection? What's happening in other parts of the world or even just the US? I wouldn't think it would be too hard to find away to give an idea of what is happening in the rest of the world without taking the focus away from the group.
That is the horror genre's longstanding problem: avoidance of logic, as they know the second you apply it to their situation, everything falls apart. This is why so many horror stories avoid going into relevant details about an alleged widespread event.
I recall some YouTube guy tried to explain how the military was "overrun" in TWD's storyline, but it did not make a bit of sense, as he was glossing over too many factors which cannot be easily explained away.
No matter how the zombie plague was spread, we live in a 24-hour information reality, so real news, false news, lies and BS can be cleared up quickly, unless the source is spreading disinformation (i.e. the government), and even in that case, leaks, basic detective skills, etc., would clue the population in on the dangers of zombies, the effect of bites, and the best way to destroy the creatures.
TWD's world did not suffer some attack which shut down all grids (and those who run them), servers, etc. Information would spread with the speed of thought, which would give many a tactical advantage regarding heavily populated areas while seeking supplies (increasing the chances of attack), morgues, hospitals, etc.
TWD simply drops the zombie outbreak on everyone like a light switched on, so suddenly, the population is scattered, lost and absolutely no administrative structure exists--even on a fragmented level. Oh, well, there was that little thing with the trained soldiers who were ambushed like rank amateurs by--of all people--the Woodbury goons.
Sure, the drama is what sells the show, and it works in several ways, but we as an audience cannot divorce ourselves from logical expectations, even in a horror story.