Why do insurance companies not pay for adult fluoride treatment?

Money: Insurance companies are in business to make money for the insurance company. To do this they have contracts that dictate what they will and will not cover. When deciding what to cover they look to eliminate as many minor procedures as possible as the least number of people will object to this. Adult Fluoride treatments are relatively inexpensive so very few people object to it not being covered.

Sadly insurance: Companies are not truly interested in the patients well-being, rather what is most economical for them. With that said, dental insurance is essentially not truly an insurance, rather a "contribution" or "donation" up to your yearly maximum. I wish i could give you a more positive answer, but they (insurance companies) are every dentists nightmare ! hope this helps.