Look at it from a cadet's point of view. £65K down, low hours, no job prospects, loan to start paying back, blinded by the propaganda that you're on an Airline Preparation Program (i.e. APP first officer or something like that) and you can see why there's a queue of young lads and lasses with a £34K cheque.
I'm not saying it's right, far from it, I'm just pointing out how they get away with it. Very clever stuff and a great business to be in. Nobody stops it as it's only affecting a minority, if affected the masses then they'd wheel in Anne Robinson (Watchdog, no not her it's the show she presents) and the faces of Airline/OAA/CTC/etc Management would be plastered all over prime time tele and portrayed as villains (come on boo and hiss, it is panto season!..."they are behind you!"(I won't go into what they are doing there)).
So what should a OAA/CTC victim do? Pay the £34K and try and make some sort of progress? Walk away from aviation until the supply demand relationship swings the other way? Buy a more sought after TR e.g. on a turbo prop? teach PPL in a SEP until you meet a nice man who let's you come fly for his aviation outfit?
Ideally it needs all graduates to boycott such schemes, but how the hell does one control that. There will always be several who have the cash or just don't care and break ranks and undermine the whole idea.