On the flip side, nobody can be expected to keep their website up for 4000 years. Hosting costs money and time, and at some point, the thing you're hosting will fall out of relevance enough to no longer be worth the cost.
This is why archiving is important. Hopefully most of the content that was lost was archived at some point. Getting a good chunk of that content onto long term storage would do future generations a favor (even if it's just a bunch of tape storage locked away in a warehouse or something).