Another factor was the war effort. There was a huge campaign to gather and donate as much waste paper as possible because it could be used to make cardboard for moving supplies. Some of the first things that would get tossed out were old comic books.

Also just in general: collector’s markets overall kinda seem to largely either be a grift or a way to do money laundering. I saw a breakdown on the “classic videogame” collectible market a while back and the rattings agencies who judge them and apparently a lot of the figures from that were also involved in the comic collectors market before the crash in the late 90s.

The short version is: most of the big sales events that happen where something like Action Comics #1 sells for a million dollars are essentially sales back and forth between a closely knit group that artificially inflates the selling point of the actual comic. That in turn creates a knock on effect where suddenly you have a huge people rushing into the market to figure out what their stuff is worth and it creates a huge bubble in the market. All the while the people who started the initial grift are making out early and everyone else is left holding the bag when the value collapses.