The fairness doctrine remains in place for electoral candidates (well, it's called the Equal Time rule or something, but same idea). If you give one "major" candidate a prime time interview, you have to offer the same treatment to the other. Trump declined the interview.

This is part of why voting third party is not a waste: imagine if 60 Minutes were legally obligated to host PSL or Green Party for a sit down interview every time they gave one of the Ghouls a time slot.