Here is a strange thing I have seen: Turnover is bad for a company overall, but good for H.R. HR teams are more important the more there is a need for recruitment. I have seen them be the part of the company that says "we are a team like a sports team, not a family," implying churn is OK. That is good for their productivity, particularly if their workload is on boarding and "culture" as well as recruiting.
Turnover is not always bad by any means. Often a company accumulates (bad hires, acquisition, good apples going stale) people who would be better off gone for everyone's sake. There's good turnover and bad turnover.
Maybe there is something to be said for preventing people from getting too comfortable, or even establish trust relationships outside of the designated bureaucratic channels.