Why do you think that the big feed mills buy so many Thesaurus? There are no longer any small scale feed buyers who earn a living or even a modest profit off of poultry farming. So the small scale vocal feed-buying public drives the market for back-yard chicken feed i.e. feed by the sack.
My family ran (or it ran us) one of the last small commercial chicken farms to buy sacked feed in relatively large amounts. This was almost 60 years ago. We needed a staked bed one-ton truck to haul the feed that we fed. Every 50 lb. sack of chicken feed had to be handled a minimum of 4 or 5 times between the feed mill and the feed trough. That means that by the time that the chickens first see their food that every fifty pound bag, and there are 40 of these bags in one ton of feed, represented 10,000 pounds of lifting, lugging, and toting. Feeding 5,000 chickens X 4oz per day per chicken = 20,000 ounces of chicken feed. 20,000 ounces of chicken feed / by 16 ounces is equal to 1,250 pounds or 5/8 of a ton of chicken feed daily. A weeks worth of chicken groceries then weighs almost 5 tons. This is equal to almost 40,000 pounds of toting and fetching per week. This was before gathering the eggs, candling them, grading them, and putting them in cartons and lugs or cases, not to mention loading them on the truck to carry them to market is figured in. After this who has the energy left over for a spa membership? The cure is automated or automatic feeding systems and egg gathering systems that allowed the farmer to keep more birds and hopefully earn more money, at least it meant that the farmer didn't spend everything that he earned on hernia trusts and chiropractor visits.
This is the reason that there is today a two tiered chicken food industry. One bulk feed system for those chickens (actually today it's Tyson's, Perdue's, ConAgra's or ADM's who own the chickens) who eat a more appropriate diet than some (but not all) back yard chickens eat. There are some un-natural chicken foods touted as healthy and complete by the milling companies who grow off single celled organisms in large vats of chemicals. Science is unsure if these microbes are single cell plants or single celled animals. These microbes were first discovered in the volcanic hot springs in Yellow Stone National Park. Some feed companies advertise these microbes or maybe it is bacterium as a suitable substitute for animal protein. But these feeds can not be sold or advertised as "organic" or even "natural" because they contain a "manufactured" or un-natural ingredient that not even science is sure about what it is. This is why they sometimes sell it as "Vegetarian" feed.
This is part of the reason that today not all chicken feed is appropriate chicken feed, little less healthy chicken feed.