"[O]nly seven states -- Alabama, Georgia, Indiana, Nebraska, Oklahoma, South Carolina, and West Virginia -- joined in friend-of-the-court (amicus) briefs supporting the plaintiffs' position that premium subsidies should be withdrawn in states with federally run health insurance marketplaces.... [M]ore than three times as many states -- 22 states plus the District of Columbia -- filed an amicus brief supporting the government's position that premium subsidies should continue to be provided in all states, regardless of whether the state or the federal government runs the marketplaces."