Are readers born or nurtured?

I have read to all three of my kids since birth. They are 13, 11, and 9 and we still have read aloud every night. We read all of the Little House series, all of Harry Potter and we are currently reading Summerland by Michael Chabon. I have done this, because experts say that reading to children instills a love of the written word and a love of reading. As a voracious reader myself, I know they see an example daily. Still while my oldest son doesn’t feel whole unless he has a book with him, the other two could not care less about a trip to the library. So, was the oldest just born to read and the other two not so much? Or did he just pick up the habit while the other two did not? What’s your theory?