My initial weight-loss motivator was vanity ... I decided to start dating, and I knew I'd be more successful if I lost some weight, and I knew I'd be more resilient if I felt good about my body.
Along the way, I started getting excited about health, and that's been a recent motivator.
After losing a significant amount of weight, I've enjoyed the drastic changes so much that they keep me going: having more energy, having a spring in my step all the time, my range of motion, my ability to break into a sprint, being able to find clothes that fit, being comfortable in many more situations, etc.