Hahaha, same here! I think it probably has to do with when they see that the initial sales aren't as expected they sweeten the deal to reach the projected sales numbers. On the other hand, I imagine these kind of campaigns are planned along time ahead... But yeah, I have the same feeling and I most often miss out on deals...
We can comfort ourselves by telling ourselves that it most often is budget devices given out as extras 
But I would love a free tablet any day! Wireless earbuds and chargers? Nah. Have so many of them laying around now...
