to be fair, everyone's teeth are different - some people just get blessed with healthy teeth, and if you don't eat messy, you might be good with a sip of water in between morning / evening tooth brushing. After all, cave men also didn't get caries in their 20-something years of life at least.
While it's true that some people inherit the genes for harder enamel, which goes a long way toward determining how scrupulous a person has to be about their dental hygiene, it wasn't until very recently that we had diets filled with refined sugar.
I'm a school bus driver and one of the girls on my bus this morning was complaining about her teeth being yellow. I asked her if she brushes them and she said "no" like I had asked her if she could fly. TBF we think her mom steals her medication so her lack of basic life skills is understandable.