In the context of OP’s post, the meaning is that it’s easy to look at the still-surviving structures from ancient civilizations (e.g. pyramids, castles) and get the incorrect idea that buildings used to be built better and more durable than buildings of today. But that’s not true, there were also plenty of buildings in ancient civilizations that didn’t last, they just get forgotten and ignored because they’re not around for us to see them anymore.
https://en.m.wikipedia.org/wiki/Survivorship_bias
In the context of OP’s post, the meaning is that it’s easy to look at the still-surviving structures from ancient civilizations (e.g. pyramids, castles) and get the incorrect idea that buildings used to be built better and more durable than buildings of today. But that’s not true, there were also plenty of buildings in ancient civilizations that didn’t last, they just get forgotten and ignored because they’re not around for us to see them anymore.