People don't need to brush their teeth as much they need to "brush" (massage) their gums. A centuries old adage to "brush you teeth" should really be "brush your gums": massage your gums to flush out the gunk between tooth roots and the gum tissue lining them. Otherwise that sliver of space becomes a garbage dump where bacteria will thrive, multiply ... and deposit a foul smelling waste. I think that space is the primary source of halitosis, and more certainly the place where gum disease starts.
If it's true that Beethoven kept immaculate teeth using a napkin, I surmise that he was actually keeping his gums healthy by conscientiously massaging bacteria food out of his gum/tooth space.
The sugary SAD (standard American diet) actually promotes tooth decay and if you eat a lot of sugar, all the brushing in the world is not going to stop it. (That goes for sugary soda pop as well).
I went to mostly a Keto/carnivore diet a couple years ago and eat virtually no sweets or processed foods. My dental checkups have gone very smoothly since even though I brush and floss no more frequently than I had been.