If you had read the last 33 pages you would see why. If you have read those pages are are still posting, you are either a troll or not particularly observant.
On the outside chance you are not taking the proverbial...
About 9 months ago I considered the various cadetships, mainly because I was jack of my current career and wanted in to aviation. I looked at the cadetships for one reason - there was some form of a job at the end of it and I needed that certainty if I was going to upend my families life to become a pilot. While I take what I read on here with a pinch of salt (because clearly the opinion is one way) after some reading and thought it was clear what the cadetships were there for, and long term I decided even if I went through with it, long term I would suffer for it.
Firstly, if there was a pilot shortage in airlines why would they take ab initio pilots when there are many experienced pilots out there that only need some CRM and type training to become airline FOs? That would be cheaper, quicker and less risk for them to get a return on investment on qualified pilot versus an ab initio.
Secondly, if they want you as a pilot, why are you paying them for that opportunity? If they want a guarantee you will stay around and give them a return, there are ways to write that into a contract without an up front financial burden. In what other job do employers out there ask interviewees to pay the costs of their own interview, let alone their training?
Lastly, you have to ask what is in it for the airline to take in inexperienced low hour pilots, when they have other options locally or overseas. This one is clear - all the various cadet schemes end up with either the cadet paying to perform labour for the employer, or entering the crew ranks as a "junior" officer on much lower pay while also paying back their training. These junior roles are typically not defined in EBAs and seem to always have special arrangements. Stop and think about this. Once they have pilots indebted to them, they can offer much smaller raises and condition improvements compared to experienced pilots who know they can command better money elsewhere.
With respect to the REX cadetship there is a question about building command hours. You might build a lot of co-pilot hours, but building command requires company time and money (i.e C&T oversight while you fly ICUS). There is a counter argument that ICUS can be built otherwise, but think about it, does the company really want you to be promoted so they have to pay you captain rates, or would they rather you just get jack of it and leave so they can put in a new cadet on lower wages. So not only are you cheap for them, its hard for you to leave and get ahead.
Perhaps you think I am being cynical. Maybe. But I have also seen enough of how companies and managerial types work to know that the above is not far fetched. The fact is when it comes to flying there is a type of person who just wants to do it regardless - businesses are willing to exploit that for their own gain.
Take from that what you will.