Handling of the HYDROFLUOROSILICIC ACID is difficult. It eats through everything, even glass eventually. Tanks need replacement regularly, you have to wear hazmat suits when working around it... Go ahead get a little bit on you... it burns like hell and cant be neutralized.
This is the primary reason coupled with the fact that most kids have easy access to fluoride rinses and toothpaste. No reason to go with a preventative dones and scale back to a maintenance dosage.
Plus the crap is getting expensive to buy and truck. When I worked at a water filtration plant a semi truck load delivery was an expensive event, and that was 15 years ago. Today it's worse with the OMG WE ALL GONNA DIE OSHA standards for safety.