The desert like imagery and dilapidated buildings were a result of a postulated post-nuclear war landscape which was a very real fear beginning with the advent of nuclear weapons in the 1940s. This fear continued to in strength where it reached it's apex at the height of the Cold War in the 1970s and 1980s. Most post-apocalyptic fiction can be traced to this time frame.
This added element of nuclear waste also leads to the introduction of mutations and mutants which also populate the post-apocalyptic landscape.
The desert setting and the sudden return to a pre-industrial age led to many elements of the Western being included into the post-apocalyptic setting.
Such films as 28 Days Later and the overwhelming success of the television adaptation of the Walking Dead, the post-apocalyptic genre has expanded to include both nuclear and biological catastrophes and the subsequent alterations to humanity. In these settings much of what humanity had built before the catastrophe remains, only in a dilapidated condition. As with nuclear mutation, in these stories the biological agents leads to forms of mutation all their own.