At this point, the story is pretty well established. Conor McGregor wanted fewer PR duties surrounding his UFC 200 rematch with Nate Diaz, considering that he had to fly from Europe to do them, and the UFC wouldn't budge. Conor bailed and the UFC pulled the plug on the fight.
With UFC 200 setting out to be one of the UFC's all-time marquee PPV events, they needed a new massive headline fight to draw in the fans they'd planned on getting with Mcgregor/Diaz 2. Enter Jon Jones, fresh off a win over Ovince St. Preux and Daniel Cormier, recovering from a recent leg injury.