Was it because of the later creation of the office? Was it due to the office of president's foreign focus?
Edit:I mean in English in Ireland, probably should've specified that in the title just to be clear...
The best reason I can offer is that it is the only one of those offices that is primarily referred to in English in the constitution. I have never seen a reason for it. I suspect it is that there was no English equivalent and therefore no need to distinguish the office.