That’s like asking why we can’t just eliminate gonorrhea… people keep inoculating each other with the bad shit.

I do tell my expecting parents (who happen to have bad teeth) that they should not test the food in their mouth and use the same spoon with their new child, as they will be passing on their bacteria to the kid. I do also imply they shouldn’t share things like drinks.

Whether or not they listen to me isn’t my problem…

It’s everywhere. You’d have to sterilize the entire planet.

Because then dentists would go out of business! 🙃

we sort of can, it’s called eating a better diet.

stop feeding the bacteria tons of sugar, start eating more chewy things that effectively brush your teeth as you eat them, and maybe even start chewing stuff like stalks of grass or twigs, that’s how a lot of people keep their teeth clean even today.