Is there no such thing as a legal obligation to bury the dead in the US?
As far as I know it's up to relatives or loved ones to bury their deceased and its up to them to arrange a funeral, plot of land, headstone, etc which runs in the thousands of dollars. If there is no one willing or able to pay then I'd assume the state essentially disposes of the body by cremation.
In my country if you no one is willing or able to pay for the burial of the ashes or the body the state pays but can get back the money from heirs and relatives. You are not allowed to not bury the ashes.
Ashes pose no public health risk (they're often scattered in public places, parks, and bodies of water), so it's surprising to learn that any government would require that ashes be interred below ground.