The labels on toothpastes and mouthwashes say to never swallow them. why is that?

Swallowing stuff: It's a basic precautionary safeguard. Toothpastes are meant as an aid to facilitate cleaning your teeth and are not meant to eat. They are safe, but in excess can make your nauseous or sick. By the way and for example, ingesting too much salt all at once can kill you.

Hazardous : Because there is nothing beneficial in swallowing toothpaste, and there are some things potentially hazardous like flouride, and artificial sweeteners !