You have listed several factors (food, water, predation, etc) as if they were all the factors.The giant pink elephant in the room called reality.
... In the picture below are two hens on their first day out that are the product of these wonderful advances in chicken keeping and chicken health. They’ve eaten nothing but commercial feed, never been exposed to the dangers of free ranging. They’ve been carefully bred with the aid of some of the best genetic science available. They’ve been kept in well ventilated and pest free environment providing clean water and constant access to commercial feed. If they are lucky they might just struggle to 4 years old, finally succumbing to one of the cancers common to high production hens.
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On the other hand here is a pair of dirt scrabbling mutts who have eaten everything from mice to Orkney mature cheddar cheese. Every day they risk predation by free ranging. Given a choice they’ll drink from a muddy puddle. No scientist has improved their health with careful breeding, special diets and ideal keeping conditions. If they can dodge the predators and keep out of fights they may live to ten, or twelve years old.
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How you keep your chickens is your choice; unfortunately for the chicken.
Chickens are social creatures. Battery hens (here, at least) are usually kept isolated in individual cages.
Limited options for mental stimulation or expressing instinctive behaviors such as dust bathing may also be factors.
This is the equivalent of feeding one flock starter pellets and water for nearly three days and another flock grower pellets and no water for nearly three days and claiming the results prove starter pellets are better.