My biggest motivation is the fresh (tasty) eggs that are produced by hens that live and eat well. We occasionally cull chickens for meat, but since we only keep a small flock, it is infrequent.
Second, chickens do a great job helping provide high-quality compost for the garden. They turn the compost pile looking for scraps and bugs, saving me the effort of turning the pile myself. And their manure is another significant source of fertilizer for the garden! It's win-win.
Third, I like knowing that I've taken one more step away from a food system that is broken. I have control over how my hens are treated, housed, fed, cared for, etc. I don't want to support farms/companies producing eggs as cheaply as possible for as much profit as possible.
Fourth is the enjoyment! Chickens are fun to raise and watch. They have definitely changed the way I think about my food.