You know, I have often wondered about this. As for me, chickens just go about chickening. However, I am a realist, and I do not expect them to live forever, and really I don't cuddle my chickens.
My chickens get a lot of fresh air, sunshine, exercise, and not excessive feed. They fly up to roosts, both in the coop, and in the run, they jump up on platforms and on top of shelters. They have good shelter in the run, but they also have open exposure. They go where they need to.
Sometimes, I wonder if people with small flocks, keep them in small set ups and they don't get enough exercise? After all, if you go to a doctor, the first thing they says is 'exercise?" Often times in keeping birds safe, we keep them in too small of set ups - especially of chicks.
Consider the difference in a three day old chick that is exposed to a misty day. This chick is took on a walk, where she/he climbs through deep grass, over sticks, and jumps small obstacles. Gets a grasshopper leg for a treat or perhaps a piece of a root. Gathers under mama for a good nap, and then off to explore the world again. Some chicks might die, but the rest are in prime health.
Compare that to chicks that are under a heat lamp, and water and feed in front of them on a sawdust bedding. Yes their needs are being met, they are kept at a constant temperature, and they too take naps. But it is a sterile boring life. And probably more of the chicks live, although, some will die in spite of this.
I have switched from the constant 95 degree temperature 24/7, light all night to a insulated box, no heat lamp at night, brooder box, I put them outside for short periods of time in the garden almost immediately. And I get them in the flock by 3 weeks of age.
Or I raise them under a broody hen, and she does all that.
I think fresh air, exercise, sunshine are good for birds. In 20+ years of keeping chickens, I have lost birds to predators, I have had birds just die. But to my knowledge I have never had EYP. Or an egg bound chicken. However, I also would not treat. If the bird is in misery, I would put them down.
Mrs K