Understandably, the corner drugstore can no longer depend upon the trade of the neighbourhood snapshot trade, but in order to supply the necessary product to any sector of the market, the product must be manufactured in quantity.
Would it be economically unfeasible to divert a small part of the production of this pure product from tank-car to litre-bottle? Would the home-consumer market be able to absorb the relative expense ratio?
I don't think the corner drugstore ever COULD make it on the neighborhood snowshoe trade. My company (employer) once owned a chain of minilabs, always thinking that if they could get large enough, then they could become profitable. Never did (to any worthwhile extent). A big problem was, my company was trying to be profitable in photofinishing, whereas the competition could often exist on a breakeven basis as a tool to bring foot traffic into a large store.
Regarding the cost of diverting some of the process chemicals into home user sizes, well, my guess is that the customers are generally too "expensive" and unreliable. If they don't know what they're doing, they might use up a couple half-hour sessions of tech support for $5 worth (cost) of chemicals. And just wait till they ruin an important roll of film and blame it on your chemicals.
And if customers don't buy enough on a predictable basis, the manufacturer may have to recover and dispose of a certain amount of chemicals, while possibly being subject to hazardous material shipping regulations. The relative profit potential may simply not be worth it. I'm just guessing, of course, but based on more process experience than you would probably guess.