Free Return Address Labels

Why do I always seem to get free return address right before a planned move? I spend months and months writing out my address by hand (b/c I'm too cheap to buy labels and too lazy to make my own, though I have the sticky paper to do it), and then right before we plan on moving I start getting free labels in the mail. What is the deal? Maybe it would help though if we actually lived at a place for a decent amount of time? With a max of about 1.5yrs at the same address I suppose it takes that long just to get our new address on all the lists, lol. I got some really cute labels from St. Jude's Children's Hospital last week. I'm thinking I"ll send them a few bucks just to say thanks :)