Kevin Humphreys (Dublin South East, Labour) | Oireachtas source

I can only speculate but I imagine a person wishing to progress into a more specialised area would choose to work part time through an agency until such time as he or she has decided on the speciality area in which he or she wishes to work. I would say there are a wide range of reasons medical doctors work for agencies. They are certainly in high demand in Ireland and across the water.