Diaz and McGregor already happened.
Point is, they have a champion publicly campaigning against everybody outside of the division he's holding a belt in. What's the point of keeping the belt on him at this point? So he has more promotional value on their posters? If a Diaz/McGregor makes sense to them, then so does Edgar/Aldo for the belt McGregor doesn't appear to want to compete in anymore.
Conor sells more if he has a belt, even a belt he has no plans on ever defending
Nate/Conor makes more money then Conor vs Frankie or Aldo
This is the direction the ufc is headed which is a terrible path