Most attrition is decided at the hire, not the exit.
The leaver was mis-hired, not mis-managed.
When a senior person leaves inside a year, the post-mortem usually looks at the manager, the team, the moment. Often the real cause is older than all of that. The role was sold as one thing and turned out to be another, or the person was a stretch-fit the assessment talked itself into. The exit was written into the offer.
That's why retention work that starts after someone joins is already late for a meaningful share of leavers. The cheapest retention lever is an honest search: the right fit, an accurate picture of the role, and a comp number that doesn't leave the person feeling underpriced the moment the market moves.