Comic book stores killed the comic book by closing off the product to new purchasers.
My first comic (pictured above), probably yours, and any number of collectors and professionals was given to me by a disinterested adult when I was home with cold. In New York we had stationery stores. These were like Hallmark stores that also sold calendars, office supplies, journals,and cigarettes. They had extensive candy counters and magazine racks. Everybody who needed a lighter, a birthday card, Playboy, or a stick of gum went into those stores. That's where my mom bought me my first comic book, next door to her beauty parlor, when I was home with a fever. She probably regrets that purchase to this day. Once I was hooked I was able to bicycle to the local stationery stores myself. I could go in and browse the revolving magazine stand of comics. Other kids were there for candy or baseball cards and grown-ups were getting pens or holiday cards or something. Comics were a quarter. Comics were cheap because they were supposed to be periodicals. They had the requisite editorial (Stan Lee's soapbox and bullpen page) and production costs were paid for by advertising. So the point is, an adult purchased one comic and started a sustainable habit that only needed a bicycle and tiny allowance. That is how a market was created in the 40s, 50s, 60s, and 70s.
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.