"The EPA said the cost of implementing the standards would range from $7.6bn to $8.5bn (£3.7bn to £4.1bn) but that would be outweighed by health benefits valued up to $19bn (£9.3bn)."
So at the end, it all comes down to money. If they had thought that the health benefits would value up to just $1bn, they wouldn't have passed this law. Read the full article