Another possibility might be that although he seemed to have a lot of experience at the outset, his ideas were finite and had already reached their horizons. In a case like that, which has happened where I work, it's better to stop at the end of a probation period before somebody gets entrenched while no longer justifying their employment. A good director must be able to see such things and take tough decisions. This is, I point out, entirely speculation, which is no more than anybody else is doing here of course.