Deeper picture time.
A person leaving a parlour might say something about the person. Or, it might say something about the parlour. Or both.
So,wanting to know why makes sense. It can and has had impact on the establishments involved.
Fired vs. quit is very relevant. Take this hypothetical - one of the stars of a particular establishment ends a lesbian affair with one of the bosses of that establishment. That boss doesn't want that relationship to end and makes life difficult for that star. Does it surprise you that that establishment seems to continue to have trouble keeping stars?
Try another hypothetical - an establishment which is really limited into the number of girls it can have in it's stable gets rid of someon coasting on former glory.
You want another hypothetical? The star of one establishment is horrified when said establishment brings in to very high maintenance stars who act like prima donnas and cut into the original's business. The original star, who months earlier had never thought of going anywhere else, finds herself travelling 3 times as far just to get away from the prima donnas. Naturally, the prima donnas don't last long.
One more? How about the star that leaves one establishment after a good number of years of service, because that establishment is catering to some of the newcomers, and goes to a rival establishment - only to find that rival establishment so poorly run with personal politics and cattiness, that she realizes the grass isn't always greener on the other side and scurries back to the original establishment! (Imagine the phone call!)
I'll leave it to your own judgment as to whether these hypotheticals are realistic or not.