The fact that we have been in a rather stagnant la nina state all year long makes it less likely that the IOD and ENSO are going to couple and mutually re-enforce one another to the same degree that they would if la nina had really began to blossom this summer and into the fall. I think this is part of the reason why a lot of guidance dissipates both events pretty quickly during boreal winter and think that makes the most sense, especially considering the self-destructive nature of ENSO in general. ENSO is an acronym for El Nino Southern OSCILLATION, which at baseline is exactly as the name implies, an oscillation back and forth. It is not meant to stagnate and there are certain atmospheric mechanisms in place to ensure that any said stagnation if fleeting. The resultant disconnect between the IOD and ENSO when the latter becomes stagnant is one of them, and the inherent dynamics of the Walker Cycle being the other prominent device that favors this oscillatory proclivity.
A crude analogy is to consider this la nina akin to a post ERC hurricane on a smaller scale in that the window of time for it to exert its most profound influence on the ambient atmosphere has past. A stagnant hurricane is less equipped to rip a hole in the ozone just as a stagnant ENSO event is not as pervasive a hemispheric driver. Tropical systems and ENSO are both ultimately self destructive to a degree...remember that.