Adding to FuglyDuck's good explanation, there's another element. Not quite all broadcast (over-the-air, non-cable television, i.e. publicly accessible for free) TV follows this rule, as talk shows are co sidereal to be entertainment and are excluded. So the FCC threatened to remove the exemption for talk shows, meaning CBS wanted to play it safe and not risk the government making this a problem, even though it's not (currently) against the rules.