ancient roads and buildings keep well but they were also very resource intensive to build. it helps to have slaves, prisoners and poor people if you're building everything in stone. the Romans did have concrete and it has kept well, and we could replicate that, but it's not practical to construct buildings in that way today. the steel bars in reinforced concrete can crack and corrode, which is a problem, but the benefits outweigh the disadvantages in most cases.
Discussion
I listen to a podcaster, Jack Spirko of The Survival Podcast, who has talked about the same thing. The effort, time, money and resources required to build something like a Medieval cathedral is too much today. And people don't have the time preference to spend two generations on building it to a high standard, as they did in the past. Now we have disposable buildings, which sucks.