[0rdinal]

From my experience, junior's tend to churn out after around three years. There are often factors that go beyond whether they felt they were treated well. Looking at it holistically, younger people tend to want to move around more. It is no surprise to me that the average tenure of a junior employee is about the same length as a degree - separating life stages in to 1-3 year periods is a mindset embedded into young people throughout their education.

I would wager that perception plays heavily into this too. It can be difficult to shake a perception of "being a junior", especially when the path to seniority is unclear or poorly defined. Plus, the "two years and disappear" ethos of job hopping for quicker compensation capitalises on companies' conservative promotion criteria (and more liberal hiring criteria). Loyalty is rarely rewarded in these cases.