Why some senior officers chose convoys over staff posts

Did some admirals retire because the next available appointment was an undesirable staff post?

Yes; some left the regular service rather than accept a staff job and chose dangerous convoy duty where they believed their skills would be more useful.

An undesirable next assignment could push a senior officer out of the regular promotion track. Capable officers sometimes preferred exposed convoy commands to administrative work ashore. The choice let them apply seamanship and command experience directly against the U-boat threat instead of accepting a desk. Wartime personnel planning reflected officer preference and professional identity as well as appointments imposed from above.