This could be in the Short Answers section, because the answer is fairly simple. Tail-draggers ( like, a DC-3 or Piper Cub) could land on grass covered landing strips. On landing, the tail ( sometimes a skid on some earlier planes) would act as a drag on the back of the plane, keep it pointed in the correct direction as it slowed and came to a halt. Tricycle gear, on the other hand, were harder to use on a grass strip- there was a good chance the wheels could jam into the ground, and the plane would flip end-over-end. On paved strips, however, tricycle gear planes are much easier to use; the take-off procedure for tail-draggers is more complex. But because something like a Piper Cub can land on a variety of places- like a field- such planes have continued to be used in many places like Alaska.

There's also the matter of speed and weight. A light plane that can take off and land at 40 mph can use a grass strip, hard to do that with a jumbo jet.