Ohio was from the bare minimum preventative maintenance and it’s cheaper to ship large quantities via rail than truck.
Chernobyl was a known flaw but buried because it was a cheaper design. Still wouldn’t have happened if safety protocols were followed.
Fukushima happened because the backup generators were on the second floor and the potential for sea water to get that high was either not considered or thought to be low probability.
It’s almost always cost demands that is the root cause which is exasperated in fiat but never really going to go away