de facto, it has been said before but it is not always that easy to "just leave".
If you have any debt in Dubai (and most of the Cabin Crew have a fair bit of debt- they have loans and credit cards almost thrust upon them from the day they collect their first paycheck. The banks have desks set up in the training college on payday.) you can't leave. It has to be paid off first. If you skip town without paying it (and crew do sometimes simply not show up after a layover) you will be thrown in jail if you ever set foot in Dubai again.
For the pilots/engineers, if you have moved your family halfway around the world to come to Dubai to "just leave" would involve taking the children out of school, possibly your wife out of her job, and moving your entire life halfway around the world- again. This in itself is highly stressful, especially if you don't have a job to go to.