Unfortunately, there is no rhyme or reason as to why some people are sent pins. Some people suggest going to the Disney website and pricing and saving some packages..Also, sign up to receive the planning DVD.. Although this won't guarantee a pin, it's worth a shot.
We went on our first ever trip last year in April at the Poly, and thought of it as "once in a lifetime". We booked originally at full price, and then the Buy 4 get 3 free promotion came out, and we were able to apply it to our reservation.
Last week I received a 40% off pin, and alas, we're going back to Wilderness Lodge... The pin was a nice surprise, but nothing I ever expected, considering the randomness of it all...