People who save a lot are typically people comforted by sitting on a big nest egg. Saving a lot for retirement and then dying the day before retirement isn’t necessarily going to be a source of regret, because they had 30 years of warm fuzzy feelings about eventually hatching their nest egg. They could have spent it all instead, and had a life full of anxiety.
You’re looking for people who didn’t want to save but begrudgingly saved at the expense of their pre-retirement life and then died before they could enjoy retirement. That’s a much smaller group.
I'm not sure. There is a warm fuzzy from knowing you are okay if things go bad of course, but how many of those who saved for the feeling would have saved less - they still would want a good amount saved for things going wrong of course but not that much.