[extra88]

The secondary food/drink sources contain fluoridation because they're prepared using tap water. If you don't drink tap water, you'll still get some exposure but if you take the fluoride out of the tap water, you won't. If literally everybody brushed their teeth with fluoride toothpaste, I don't know if adding it to the water would still be worthwhile; it might be good for very small children before they have enough teeth to start brushing.

As already stated, fluoride is cheap and safe in the water. Other substances aren't cheap, have risk of overdosing (possibly only for people with sensitivities), or are readily supplied through diet. Some substances may also not be transportable through a water system because they too readily bind with others or don't remain in suspension long enough to reach your faucet.