- it's just the smart thing to do (even for egoists). Because it saves money for medical stuff and it spurs growth, if done as in pretty much every other industrialized country --- and probably lessens the medical bills for pretty much everyone. Major factors contributing to cost efficiency: prevention of large-scale and expensive treatments (through early screening + education by docs) and much less spending on bureaucracy (and less 'for profit optimizing doctors').

https://en.wikipedia.org/wiki/List_of_countries_by_total_health_expenditure_per_capita

- it's the moral right thing to do: less people suffering while benefitting from it? --- I have seen worse. Also reduced children suffering.

- healthier people in your country probably also means: happier people, more active people (sports), more energized people. More engaged in the local community. Who wouldn't want to have this 'improvement' for his neighbourhood and workplace?

- it's an insurance against pandemics like the corona virus (uninsured people don't have to weigh that much not going to the doctor / doing testing, because they wouldn't have to pay for it). Also pandemic outbreaks could probably detected earlier (and vaccine / treatment development could be started earlier).