I would hazard a guess it's mostly to do with the transient international population that make up the bulk of the Middle Eastern airlines' cabin crew workforces.
The job is fine for most for one to five years- longer than that, up comes the question on do they want to be in their home country, with their family and settle there, or move on to another opportunity elsewhere.
Also, most of the countries that employ foreign crew don't overly encourage one to have a lifeling career and retire there- most would likely want to return home & establish a solid base & life (with employment) before thinking about retirement (unless they managed to save a LOT of money by working overseas)