Point 2: The area is nuked that too much radioactive particles will kill including humans. So no one can live the nuked area for years.
Point 3: As the soil is contaminated by the radioactive particles, the soil could not grow crops. All plants turns to lifeless.
Point 4: All the effects wear down very slowly. Especially the natural bomb- The Uranium Bomb that requires millions of years as one half-life. One half-life meant half of the radioactive particles had decayed. When all have decayed,the radioactive particles are gone and life starts to grow back. Sadly,half-life is something no one could control.So let nature take its course. For the half-life of uranium-http://en.wikipedia.org/wiki/Uranium