In fairness, a lot of content created over the past 25 years or so only exists in ephemeral digital form. Some is captured in sources that libraries subscribe to but a lot of it isn't. (Of course, libraries also subscribe to content that was never on the open web.)

It's also the case that pre-web, a lot of that sort of content was pretty much lost to time. Per a discussion, a little while back, relatively little from the BBS era is preserved because it was mostly a distributed group of hobbyists.