Mainly I just don't see the point in upgrading when my existing device (currently) works perfectly fine. It's less about cost and more about waste, and good old fashioned stubbornness. Most of my books are physical; I mainly use the Kindle for reading free ebooks (like those from Standard Ebooks) or I will occasionally buy an ebook when ordering physically is impractical for whatever reason. So any slight annoyances that come from using an old device don't really bother me.