I was a PA31 instructor in 2004/2005, at that time we had a high number of applicants come in and back then give a verbal agreement that they would be around for a year. More than 50% of these individuals never had any intent on staying, it was a means to get their multi time to get on at skyw or horizon.
After that the written agreement started, you might be surprised to learn that with the amount of offline training required in the PA31 prior to the checkride that the cost of training an individual is almost in line with a turbine aircraft.