Why Custom driver access sample make the Fx2Device class's constructor and deconstructor as an private method

Question

i am fuzzy with why the sample make the Fx2Device class's constructor and deconstructor as an private method and give a public static method to call the constructor...what is the benefit?
the code fragment as follow:
Public ref class Fx2Device sealed
{
   private:
    //.......
    Fx2Device(IDeviceIoControl* DeviceControl,String Id);
    ~Fx2Device();
  puculic:
    static FromId(String id);
}

hope some one could give me some hint.....thank you