Hydro disasters have been large, but are tangible/sensible, immediate, and resolve relatively quickly (days for rescue, months for recovery, possibly a few years for rebuilding).
Banqiao is now home to 17 million people (after 40 years, largely achieved within a decade or so). Meantime, Chernobyl still hasn't seen complete containment (after 34 years), and Fukushima hasn't begun initial cleanup (after 9 years). The two nuclear sites will be obligatory nature preserves for centuries, containing still-lethal risks.
The specific failings at Banqiao were virtually all managerial and political, not technical; poor engineering, inadequate safety provisions, underestimated environmental and operational risks, poor contingency planning, unforseen perfect storm (literally), severed communications, insufficient warnings, no community disaster preparation, inadequate rescue and recovery. None of these failures are specific to hydro, all apply to nuclear power, and as non-engineering problems there is no technical fix that makes them go away.
In Banqiao, about 25,000 people died in the immediate innundation. Another 150,000 died in the following weeks of starvation and disease. There's no great mystery as to how such deaths are avoided: floodwaters are mitigated by high ground and evacuation centres; starvation and disease by food, water, and medical stocks; and rescue & recovery by trained teams and equipment. Reestablishment of communications, transport, and utilities is critical.
China at the time was desperately poor, politically dysfunctional, and gambled hugely on risk and lost. Other major hydro disasters tend to share these traits.
As do many regions looking to nuclear power for salvation.
(I've mentioned Banqiao several times over the years on HN. It's a terrifying but educational tragedy. https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... Wikipedia article recommended: https://en.wikipedia.org/wiki/Banqiao_Dam))