It's also important to note that not all medieval and historic structures survived the test of time. A case of Survival-Bias. As the utility requirements of the structure may change over time,there is no incentive for engineers and clients to design a structure that would last more than 50-100 years. As far as the current building design provisions and policies go by, rebar does it's job.

What needs intervention is to find a suitable replacement for concrete/cement citing it's increasing contribution to global warming.