20 years ago, so long as a comic book series continued to be published, its back issues retained or increased in value. The longer a series stuck around, the higher its lengthening backlist climbed in value. By the time a series hit its 50th issue, the first two dozen issues were usually fetching anywhere from 20% to 100% over cover price. These steady gains incentivized retailers to order extra copies of new issues to hang onto because if a fan enjoyed the 50th issue, they might eventually want to pick up issues 1-49 as well. Of course, there was still plenty of risk in ordering comics but those steady gains in back issue value were little rewards retailers got in exchange for ordering enough non-returnable copies of a title to keep it alive.
It was a nice little system until about twenty years ago the publishers got greedy. They saw how much retailers were making from back issue sales and decided to cut themselves in too. So instead of waiting until back issues were too expensive for fans to easily collect a classic story a la the X-Men's Dark Phoenix Saga or the prohibiitively expensive early issues of evergreen series such as Amazing Spider-Man, The Avengers or Captain America, they decided to collect and release every story they published in trade paperback, often mere days after the final chapter of a story arc arrived on retailer shelves. This proved to be a double whammy for retailers because not only were being asked to double-dip their risk by ordering relatively high ticket trades collecting the same stories they'd recently ordered as single issues but also because having all those recent stories suddenly available to read in collections meant the bottom fell out of their back issue market.
It wasn't long before publishers of all sizes were incorporating these instant trade collections into their business models because trade collections required almost no new creative content and they could cut retailers out of the transaction entirely by selling those same collections on Amazons!
Unsold single issues containing individual chapters of a five or six issue story have become as perishable as supermarket produce. Dollar bins are no longer reserved for lower grade, decades-old single issues; but also comics that are only a few months, or in some cases, a few weeks old. In short, if a new issue is not considered by collector's to be a "hot" or key issue, it is now effectively worthless. And the poor retailer who had previously seen back issues make up 70, 80 or 90% of their profits, now has to hope that the same people who once came into their shops six times to buy six single issues, aren't now clicking a couple buttons on Amazon so they can have the trade collections of those same six issues delivered to their doors at a bigger discount than 99% of small independent retailers can afford to give.
Yes, digital sales do chip away too, but I think digital readers are inclined to buy digital comics for a different experience than those who would buy single issues or trade paperbacks. If anything, it takes longer for a new 4 dollar comic to be discounted on ComiXology than it does for a print comic to be available for less than wholesale at many local comic shop dollar bins.
The takeaway is that publishers need to stop milking every penny out of retailers. That's why Sitcomics will never release low-cost trade paperback collections of our Binge Books. You want to read our stories in print, then go to your local comic shop and buy them. Amazon doesn't need the money, local retailers do.