Somebody needs to mention that really low turnover can also be a sign of problems. People don't often leave jobs where they're asked to do very little. It can be a sign of a lazy, unambitious culture.
The last place I was at had an extremely low turnover for precisely this reason. The devs had all been there for 8+ years and didn't really have to do anything. The bar was set so low there was no motivation to leave. Managed to stick it out for 6 months before I ran from the place.