The biggest problem in discussing the decline in T's & C's, and the most likely reason, is that RYR's shareholders don't give a toss. Look at what the shares have done over 10 years. They are all licking their lips with glee and don't give a fig. If RYR can continue to expand, as they must to remain so profitable, and they can crew the a/c on any given day, the shareholders will not support a reduction in profit to improve T's & C's. Turnover of flight crew is of no concern of theirs. If that model works, then they so be it. It will only be when profits are hit by stagnant a/c that someone may start using questions.
Market forces etc. RYR a flying school? perhaps. Do they like it? perhaps. Is it sustainable? perhaps. As long as the queue of cadets is there, and the pax, then they will soldier on.