I got my Kindle about two years before iPad existed. Portability of books away from home was the priority. If iPad had existed, I wouldn't have bothered with my first Kindle, because I prefer backlit to e-ink and a reading light.
Some people want an e-ink reader as well as an iPad because they have probs reading for extended periods on backlit devices. Some prefer a smaller size for extended reading.
I like my Kindle Fire for reading because of the size. Reading is my primary hobby. Some people probably think buying a device just to read is odd, but I think it odd that people pay for TV, for instance. I don't watch it. Just a matter of personal preference.