Not so sure about Banquiao, at it "took place during the Chinese Cultural Revolution when most people were busy with the "revolution" https://en.wikipedia.org/wiki/1975_Banqiao_Dam_failure

The "Cultural Revolution" began in 1966.

In such a context an otherwise avoidable catastrophe may happen.

This Revolution followed the "Great Leap Forward" ( https://en.wikipedia.org/wiki/Great_Leap_Forward ), with famines. "In the subsequent famines of the early 1960s popularly attributed to the Great Leap Forward, Henan was one of the hardest hit and millions of lives were lost." Source: https://en.wikipedia.org/wiki/Henan#Modern_Era .

Moreover all this came after a civil war and violent Japanese invasion, during which dams were bombed, causing "massive flooding in Henan" (same source).

Predicting and adverting this catastrophe was possible, but given such a context nobody was able to do so.