Low churn is generally a good thing. And having employees that stay faithful to the company 15, 20, 30+ years surely is evidence of a flexible attitude and high motivation.
However it also bears a downside: Knowledge is concentrated in those, that are with the company the longest and with it comes a certain degree of having fix-set ideas on how things must be done. And a high rate of assumptions as to what newer colleagues know - or “ought to” know.