A particular problem with cadets. Also they are often not interested in taking a further bond to be promoted and leave at FO level.
For a 20-25 year old that's a good option. Once the honeymoon period has finished and the glamour has worn off a bit after all those early sign ons, 4 sector days and back of the clock sign offs.
They're still young enough to survive a 5-15 year wait for an upgrade at a major airline, and highly attractive to the recruiting department as well.
Total package wise, a Captain with a low cost is about the same as an F/O with BA, QF, CX, EK etc. Overall they should be well ahead financially at retirement with the majors.
Should they stick around for promotion and want to stay in the left seat with the next employer, things are a bit more limited. DECs not always hired or welcome in the better companies, and they don't have any wide body time in the log book. Contract positions, often far from home, with little chance of progression, may be all that's on offer.
Grab a permanent job with Emirates, joining as an F/O but B777 skipper in seven years vs upgrade at low cost, 2 years in the left seat and a renewable contract on the A320 with Vietnam Airlines. I know which option I'd take.