The recipe for the catastrophe is design + time, so it's not like "new designs have fewer failures" offers much comfort. Of course they would.
Plus, previous installations had fewer potential non-design-related issues, such as terrorism, which (in today's nihilistic "more possible damage, including innocents and even myself" way) wasn't as much a thing in the 60s and 70s.
At least damns damage only the area relatively near them. The implications of a nuclear catastrophe can impact thousands of miles around, including major cities.
Dams are built on large rivers. Inundations resulting from dam failures tend to follow the path of the river. Cities are also built near large rivers. The Banqiao Dam failure displaced fifteen times as many people as the Chernobyl and Fukushima Daiichi disasters combined. The impending failure of the Mosul Dam is projected to do the same.
