To be honest I'd say that it's driven much, much more by compensation rather than that being some additional element. Leaving aside FAANG levels of compensation

To be honest I'd say that it's driven much, much more by compensation rather than that being some additional element. Leaving aside FAANG levels of compensation, places pay staff the minimum they can get away with and don't raise existing staff's compensation unless absolutely forced to. If you could somehow anonymously go through your company's hiring process you'd be offered more as a new joiner for your skills and experience than someone already there, which is bizarre set-up (even though any new joiner has to spend time ramping up & existing staff have a great level of instituional knowledge). So companies have created a system where if you want to get a fair market rate, you _have to_ move every 2-3 years. I know a lot of people who stay put in spite of this, as they don't like the friction/effort of interviewing & are comfortable/like colleagues etc. If places paid market rate to existing staff, I'd imagine their churn would plummet.