The IA has tried distributing their stores, but nowhere near enough people actually put their storage where their mouths are.
Typically because most people who have the upload, don't know that they can. And if they come to the notion on their own, they won't know how.
If they put the notion to a search engine, the keywords they come up with probably don't return the needed ELI5 page.
As in: How do I [?] for the Internet Archive?, most folks won't know what [?] needs to be.
Well, OK, maybe other webpage archives don't work as well, I haven't tried them, but there are others. And they're newer, so don't have such extensive historical pages.
Large numbers of Wikipedia references (which relied on IA to prevent link rot) must be completely broken now.