They definitely require routine maintenance and inspection.

The Nondestructive Testing article I linked to in another comment said "significant environmental damage requiring repair typically occurs before the average bridge reaches mid-life."

Spoiler: they don't, yet they do, Theseus' ship-style. For all the centuries-old bridges still in use around here, there's only a few bits and pieces left from the original, the rest has been replaced multiple times over as a part of maintenance.

The difference here is probably maintainability: for a stone arch design, you can prop it up for safety, replace a few stones, and voila, like new. For a cable-stayed and/or concrete design...not really. In other words, the bridges that have "lasted for centuries" have hot-swappable parts ;)

Lifespan, not age. Most bridges where built after 1945 with a life expectancy between 70-75 years.

https://www.nde-ed.org/AboutNDT/SelectedApplications/Bridge_...