Earlier quoted context omitted.
Man, I’ve been in castles that are less than a thousand years old that are barely recognizable. Machu pichu is a good one as well.
Castles that stay above ground, yes, but there likely would be some buried structures, too. Pompeii looked remarkably fresh when dug out.
The point stands, most things don’t survive all that long (in the grand scheme of things). Occasionally, the conditions are exactly right to preserve something, but there is a limit.