While CASA exams may be a part of the issue I don't believe they are the main issue, the real issue is that most of those who drop out don't put in the effort.
Fee-Help and university pilot courses have lead to a dramatic increase in the number of students who are doing flight training not because they have a real passion for flying but because it looks cool or because being a pilot looks great on tinder (they and there potential matches don't realise that once they graduate, they'll be heading up north to Alice Springs or something....) this 'coolness' quickly wares of once the exams come around especially CPL exams in a full time coarse where your often doing an exam every 2 weeks - i've been there and even I felt like giving up at 11PM the night before an exam!
Before fee-help with the amount of investment required only the passionate (and crazy) took up flight training and most of these people get though. Don't get me wrong some of these guys who take it up just because its cool do succeed but many don't.
Don't get me wrong fee-help is a good thing, I would have never took up this career if it didn't coming from a regional town with no flying school and a disadvantaged family funding my flight training would have been impossible.
BTW i'm an instructor at one of the fee-help schools and we can all tell by about week 2 who wants to be there and whose going to finish.