Despite the fact that the farmhouse originally appeared in only five issues of the comic book on which the series is based, the showrunners decided that we needed to see a whole season of people arguing in a living room. Oh, and the farm is run by a crotchety old man and his hot daughters, meaning the show is cribbing both from a comic book series and your great-uncle's dirty jokes.
As it turns out, the reason behind taking less inspiration from George Romero and more from The Waltons stems from a huge budget cut that the network imposed on the second season, before the pilot had even aired. The studio also provided the note that half the show should take place indoors, presumably to both save them money and make the harrowing, blood-drenched end of human civilization more warm and cozy.
Because that's what people look for in zombie stories: exquisite tablecloths.
And Mad Men is somewhat to blame here -- "entire hordes of zombies" became "maybe a zombie, every once in a while" thanks to Don Draper's love of big budgets, fancy suits, and herbal cigarettes. Arguments over these budget cuts contributed to the show's creator, Shawshank Redemption director Frank Darabont, being fired and replaced by some people whom we're reasonably sure had absolutely nothing to do with The Shawshank Redemption. So great move, AMC; fire the guy who made the most beloved prison movie of all time one year before your show moves into a prison. That's the real river of shit.