Another large part of this is that APRA have been a toothless...

Another large part of this is that APRA have been a toothless dog for a long time. They need to show some results and justification for their existence. You can bet your bottom dollar they will throw every resource at anything they can deem a "Reasonable probability" of prosecution. 

The other other thing you have to remember, is that there are a WHOLE lot of skeletons in the closest for these financial services businesses. If you think they only have one major breach to be accountable for, you are seriously naive. The regulators simply do not have the time or resources to look at everything, it's an impossible task. So if they decide to shine the light on IOOF, just the same as they are doing with AMP, expect more to come out of it.