> Poor people in the US are capable of using fluoride toothpaste and flossing. At least at homeless shelters at outreach things I’ve been to, toothpaste and toothbrushes are freely available. Your argument hinges on them being incapable on the whole and needing a Benevolent But Superior Intelligence to provide an alternative for them.
This is so incurious. Obviously most people, poor or not, have access to fluoridated toothpaste and toothbrushes, and can brush.
Yet OP cites data (not explicitly, but you can start here: https://pmc.ncbi.nlm.nih.gov/articles/PMC6974062/, there are many like it).
Fluoridated water makes the most impact on poor and undeserved communities: Why?
Is it because poor people are less capable of brushing or have less access to fluoridated toothpaste?
Is it because poor people are poor because they have poor self control, which prevents them from regular brushing?
Does it matter? Nothing hinges on them being incapable at all - your conjecture can be as uncharitable - poor people are dirty and incapable - or charitable - poor people have less money and time to seek dental care, have higher rates of untreated mental and physical illness i.e. ADHD, disabilities that interrupt daily tooth-brushing routine - as you want.
But the result is still that if we want children from poor families to have less cavities by the time they reach adulthood - we should fluoridate the water! If you trust the western medical establishment, it's broadly safe. If you don't, then none of the evidence above matters to you anyways.