As the article states the newer stuff does not have the scarecity that the Golden Age and thus and not worth as much.
The 90's killed much of the comic book collecting market. Marvel and DC fed speculators hunger for variant covers, limited editions and multiple lines of books with the same characters.
I can remember going to a comic book store in the early 90s when the Death of Superman issue came out, hoping to snag one of the coveted issues sporting an all black bag with a bloody S on the front. My 8 year old self was basically laughed out the door, saying they'd all be bought up or were selling for multiples of the cover price. That really killed a lot of my spirit for collecting. I just recently got back into comics, but purely for the enjoyment of reading them, so I buy digitally nearly 100% of the time.
Digital comics are interesting, they remove the speculating, collecting and coveting of comics for some perceived monetary value and put the content front and center, which is where it should be.
Meanwhile, for comparison, a market like Norway, with 5 million people, have at various times had multiple series selling more than 100k copies a month. Donald Duck & Co. for a many years sold 150k copies a week.
More importantly, readership here is usually estimated at 3-5 readers per copy, as opposed to more than one copy per reader in the US, as copies would pass around the family and get lent out to friends.
In France, some new issues of the top selling album titles, like Tintin, Asterix and Spirou et Fantasio, have sold in millions in France alone.