I will flip your question up the other way. Why do the operators want cadetships given the overwhelming preponderance of evidence that there is no shortage of qualified & capable pilots in AU & NZ?
The truth of the matter is there is an industrial agenda - by the operators.
There is nothing wrong with the concept of a cadetship, when there is a genuine shortage of capable skills. This is the way Asia & Europe operate, with limited or no GA industry.
The problem with some of the touted AU/NZ cadet schemes is:
(a) Off-the-shelf self training available right now at your local flying school.
(b) Potential pilots that cannot afford (a) are force to purchase the expensive (roughly double) airline training system package as a cadet.
(c) The operator conveniently extends a credit system to support (b).
(d) Because of (c), the operator can pay well below industry T&C's.
(e) Because of (d), the cadet cannot save enough to "buy out" his debt to the operator.
(f) Because of (e) there is ZERO industrial leverage, or the ability to move operators, ie indentured slave.
(g) When the debt is finally repaid to the operator, and (f) is no longer valid, their contract is not renewed , a new recruit at stage (b) is introduced to perpetuate the system (happening right now in Europe).
(h) Because of (g) there is mass of experienced FO's all looking for an operator to give them a command with downward pressure on T&C's.
The operator laughs all the way to the bank as they get a revenue stream from the overpriced training & flood the pilot market with low experience pilots to place pressure on T&C's.
The incentives to over-train pilot numbers is enormous, the only limit being the number of victims applying to join the "system".
I hope that clears it up for you Gas Bags.