I smoked cigarettes (and other stuff) from high school until I was 25. When I got connected with God through faith in Christ, He took away the other stuff, but the cig's were a hard habit to break. I'd leave the house determined to go the whole day without a puff, then stop to get gas, and find a pack in my shirt pocket (didn't even realize I bought 'em!).
Only after really learning to rely on His strength was I able to break free.
I'd say good reasons to quit are just what you said, GR8atta2d - to be around for your kids and family. Also to be in better health WHILE you're here so you can do what you do better - like dragging a big buck out of the woods