Millions of individuals pay for it now, yes, as a collective investment which pays off many times over a couple decades later as the public does not have to pay

Millions of individuals pay for it now, yes, as a collective investment which pays off many times over a couple decades later as the public does not have to pay for the societal damage caused by widespread lead poisoning. That would be both a decrease in crime, and in an assortment of health issues. The benefit realized down the line would be impossible to reach by each homeowner acting individually, as not everyone would be able to pay (and the people least able to pay statistically are likely to have more children!), so by having millions of people pay for it, we reach a better result. This is IMO an example of a success of government.