How do people just pick up and move, and leave their pet behind?

http://www.theanimalrescuesite.com/c...faces?siteId=3

Kirby was left in a house for one week without food or water when his owners simply moved away without him. He was rescued by neighbors and brought to an adoption group where I found him. He's a cuddly, playful, blissful guy who is now in my happy home with two other rescues. Always, always rescue!