IBF first cause IBF were a$$holes and didn't leave any serious time to Fury to fight his mandatory (Glazkov) who were pushing aggressively for that title shot
Then WBA and WBO cause Fury always pulled out of his mandatory rematch, tested positive for PEDs a year before the Klitschko fight or so, he also coked out and got fat. So it was a wrap for him and he's still in this semi retired position where he sometimes vows to come back but actually he's more than 350 pounds.
WBO belt went to the winner of Parker vs Ruiz, no real surprise that the WBO didn't even try to throw their belt into Joshua vs Wlad, considering that Andy Ruiz Jr. who fought Parker for the title is a Top Rank fighter