It took me too many unnecessarily drilled and filled teeth by overzealous dentists to realize this. I removed salt-sugar-fat junk food from the diet and care about my teeth. Absolutely nothing happened with them for one decade now. Again... bloody dentists, they abuse so much the fact that you trust them. They treat your teeth as a piece of sandstone until there is nothing to drill into anymore.
Unfortunately, here in the US, the elderly are often completely without any sort of dental coverage.
Which means they can’t afford to do anything besides watch the teeth rot out of their head when problems start showing up, leading to far worse and even more painful and expensive problems.
Even as far back as ancient Egypt [1]. And they had dentistry too [2]! Any time in history where they milled grains into flour with stone, you can see this pattern. In fact, it can be used to differentiate certain agricultural vs non-agricultural populations in the archaeological record [3].
A century ago is probably pretty close to the worst possible time: starchy diets, relatively cheap pure/refined sugar, but no modern dentistry.