None of these 4 reasons (TD;LR: you waited until the exit interview, you assume mentors want to manage, you assume the natural ascension of developers is management and not higher-level IC roles, you aren't supporting them and their career) are why they quit. People quit because the modern, zero-loyalty, everyone-for-hire company does not provide a long term strategy for providing intrinsic motivation (autonomy, mast…
People quit because the modern, zero-loyalty, everyone-for-hire company does not provide a long term strategy for providing intrinsic motivation (autonomy, mastery, purpose); they don't want to pay for retention and therefore don't provide perks for retention.
The culture around ROI is a massive factor. Too short? Too long? It has to be balanced.Another belief I hold: most people want to be told what to do.. to a certain degree. That's the trick.
The political way of phrasing this is that leadership also has to be balanced. Too much results in predictability and people getting bored. Too little results in people feeling lost.