As a professional in this field, top reasons would be…
Dissatisfaction with pay
Limited/No career progression
Dissatisfaction with environment/culture
Dissatisfaction with management
Poor work-life balance
Poor job design/expectations of role
Poor taining quality/knowledge management
Inadequate tools/systems
Edit: I should also point out we have about half a dozen ping-pong tables scattered around my work and our turnover figures were bang on average for annual benchmarking against the sector. I consider the average too high, though, and will be targeting better retention over this year. We’ll need at least double the amount of ping-pong tables.