There’s other factors than just brushing your teeth but brushing is probably the easiest factor that most people can reasonably take control of.
Genetics, obviously you can’t do much about. But you can avoid sweets and decide not to get pregnant (hormonal changes during pregnancy can cause mouths to get more acidic and make plaque harder to remove, and can also soften the gums and bones that hold teeth in, or even weaken the teeth directly). Also, if you want nice teeth, it’s especially important to abstain from smoking crystal meth. And that’s even more important during pregnancy.
But telling everybody “brush twice a day for two minutes” is a small ask with huge returns.
This really should be on change.org.