Comic book stores killed the comic book by closing off the product to new purchasers.
Then came Heroes World. A comic specialty chain created by Marvel comics. The first step towards Marvel's eventual bankruptcy. Following Heroes World was the creation of the the independent comic book stores. Would anyone's mom walk into a comic book store? Remember the direct sales box replacing the bar code on the cover? As a collector you wanted the direct sales cover. The magazine rack comic sales at other stores declined and they had no incentive to keep supplying them. Because of direct sales, the advertising decreased in the magazines, and the costs went up to cover production. In no time at all comics were over a $1. Comics were becoming a specialty product in a highly segmented product. A 10-year-old could not get to a comic book shop. The stores also attracted the older collector. Little kids and moms were intimidated by the stores (comic book guy) and priced out of the product. No gum, no baseball cards, no new purchasers. Cigarettes were doing a better job attracting kids to their product than comic books were. Comics, instead of being something every boy had at one time (with quite a few of us continuing to buy), became nerd fodder for older kids. Then the number 1 frenzy, the multiple cover fiascoes, the metallic covers, X-Everything, etc., all to feed the direct market. The market continually skewed older with less replenishment. To keep that market the stories changed. Who and how they hired creatives changed. These things we still talk about. Does a modern 8-year-old even see a comic book besides an Archie at the grocery store. The movies sell coloring books in grocery and toy stores, but the comic book now comes later, needing to have an ironic charge so as not to be kid stuff. Sales have shifted to the $15 trade paperback, and ironically, they are sold in real book stores. The comic book stores are closing.
So that's why we lament the loss of the early silver age comic book charm and wonder at the skeeziness of the modern independents. It's Heroes World's fault.
I'll keep an eye on this site http://www.comichron.com/yearlycomicssales/1960s.html to see if they post data to support my argument.