I think this goes back to whether or not they have emotions. Reptiles just don't have that capability. They can grow to trust you in a sense - because they know you bring them food and water and you haven't harmed them so they eventually stop seeing you as a danger. They sometimes do get attached to a person in the way that they get attached to their habitat or cage mates - in that they hate change and automatically see any new caregiver as an enemy. But a true emotional attachment to a person or even another reptile is beyond them.
I think because we love them, when they come to us without fighting, or to share our body warmth, we want to veiw it as though they love us too.