Yes, that's exactly the same what Sumerians did say back a few 1000 years ago. Why keep all these clay tables about ordering wine? Who is gonna be interested in that kind of stuff in 10 years?
Don't you think that such an archive would offer a nice glimpse into our current culture a few hundred years in the future?
Your argument is sound though. Comments on websites, even if filled with trolls and fakes ought to be treated with respect and saved for posterity, since they give an important insight into the current zeitgeist.
Here's the point: if you put some of the great content that was created there 25 or 30 years ago in front of the current generation, what is the general reaction? A yawn, that's what.
It might be fascinating in a few thousand years, but I won't be around then, and the planet might not be either, so why should I care?
I guess it has more to do with "Focus", and that comes before "Nostalgia".