The effort to create something has always factored into the price. It's not the only factor, but it's there. Additionally, I take the main point of the response

The effort to create something has always factored into the price. It's not the only factor, but it's there. Additionally, I take the main point of the response of "trivial" (in the case of typesetting it's often just providing a bundle of extra tex files to recompile your paper with) as less a remark on the price, and more a remark on the work. The question you answered was what work the publishers are doing, with the underlying qualifier of [to justify/correlate with their price] and the direct followup you didn't speculate on asking about what they charge for each item of work. It's like answering "what do doctors do to command such a high price?" with "scribble on a piece of paper". OK, let's assume that's really a good description of the work they provide, how much specifically do they charge for it? The full fee? Great, this exercise wasn't helpful at all. Can we break the work down into smaller units and try to estimate costs for each, whether those costs are "reasonable" or "unreasonable"? When I pay $30 for a single paper, what parts of the work endeavor does each dollar go to? We can even take into account fuzzy second-order fees like "well you're really paying back into the massive amount of work they did beforehand so they can scribble the right things now" when we're out of other ideas, but I can't imagine much of that $30 going specifically to the work of "typesetting" because it's so trivial.