The Walking Dead: A Decline in Story Telling

This topic would explore why The Walking Dead became so successful as both a comic book series and a television series, and how its story has suffered such a drastic decline in actual plot development since the Prison Arc. A major cause that would require further research might be the fact that the story has no end because the virus overtaking the world cannot end, and thus, the horde of zombies will never die; so the question to ask is, can a story continue to be interesting if the main conflict cannot be resolved? Of course you have an onslaught of new villains every few seasons, but by and far they are not different characters by any means.