Nine years.... that’s a heckuva run. Like most series though the producers beat it into the ground instead of stopping before it all gets too old. I never watched it after the second season.
After the first year, you have all sorts of real world issues, like the real effects of human society breaking down.
No more new stuff getting manufactured, which means stuff which gets old, rots, or breaks can't be replaced. Stored food reaches the end of its shelf life. Canned food can last a long time IF properly stored, but in abandoned houses will be exposed to weather and cans will rust.
By year 5, surviving people would be in bad shape.