PINS tend to go out to folks if they do something like go to WDW one year, but don't book a return trip the next, or the following year. Disney offers them a PIN as a way yo lure them back. You don't tend to get PINs if you currently have a trip booked.
There is also a chance of getting aPIN offer if you price outa WDW vacation, but don't book it, and also if you sign up for all of WDW's email promo memberships...
I should also add, not all PIN offers are the same. Some PIN offers are smaller than publicly offered discounts. Others are the same as publicly offered discounts, just offered a little bit earlier.