Don't forget GSP, Couture, and BJ, all of whom gave up their newly won titles rather than defend them.
BJ and GSP have been addressed, Randy doesn't count based on my admittedly poorly worded qualification that they must 'never' have defended the belt in that weight class.
Essentially there are tiers:
Tier 1: Randy. Vacated but returned to win and defend the same belt.
Tier 2: BJ. Vacated for money and to fight even bigger guys. Returned to fight for the same belt against the two best guys in the same division.
Tier 3. GSP. GOAT of his weight class, but gave up the other belt because he didn't want to fight contenders.
Tier 4. Conor. Currently hasn't defended two belts, but first one is no big deal since he moved up to win a title and could still do it. Moves up or down depending whether he ever defends this belt.
Tier 5. De Random. Plainly pussied out of defending a belt.