The Bivol rematch might happen next year or maybe we will not see that happening at all as Canelo is with PBC now. Bivol is with Eddie Hearn and Match room so I doubt that they are going to work out as Canelo's contract with PBC is exclusive for a 3 fight deal.
Canelo is scared to fight with prime Bivol, so he avoid it and choose to fight with the opponents he think he will win e.g. Jermall Charlo, David Benavidez, and David Morrell. If the undisputed light heavyweight will happen e.g. Bivol vs Beterbiev, if Bivol win, Canelo will wait until he move to heavyweight or retire. But if Beterbiev win, I think Canelo will dare to fight with Bivol since both of them don't have any belt and the judges will favor on Canelo.
David Benavidez is not on Canelo's option as he is hiding behind the reason that there's no benefit for him if he will fight David, which is true, but considering that he's also fond in cleaning his own division, I cannot see any reason why he will not give David the chance and this governing bodies is not doing their job and give a mandatory fight as David is a WBC interim boxer.
That's what Canelo also said against GGG, that he will not give GGG a rematch. But when GGG went to DAZN and sign a contract, Canelo has no choice but to fight him. Same in the case with Benavidez now, Canelo signs a 3 fight deal with PBC and Showtime, so it means that they are not under Al Haymon and PBC. So I wouldn't be surprised that Benavidez is next after Charlo. So he can't hide from his reasons of "not fighting another Mexican".
For Bivol, I think Canelo is not after what Bivol is holding right now as a rematch is just a plain fight to redeem his loss and so it doesn't really matter if Bivol will lost the belt to Beterbiev or not. But as per Bivol's words, there will be no rematch unless Canelo wanted to take a risk and host the fight at his own division.
According to Bivol's camp, they offered too low for their rematch, that's why it didn't happen. So first reason is money. Second, as I have stated, Bivol is with Matchroom and Eddie Hearn, and now Canelo is with PBC and Al Haymon. So we all know that most of the time, boxing politics hinders us boxing fans from seeing great fight and so we might not see a rematch anytime soon.