Thanks for this gen. It was largely me who raised this matter of sparse services: I'd thought that it was a consequence of the fuel-related woes from the early 1940s onward, and had no idea that -- as you recount -- it was a pattern which had started out in the Free State, almost from the beginning of that entity's existence. On reflection, it would seem of a piece with the Great Southern Railway (formed 1925, from all railway undertakings whose systems lay totally in the Free State) being generally described -- one gets the picture -- as, overall, in the main a rather drab, grey, unenterprising and apathetic outfit. And one learns that CIE, its successor from 1945, acted similarly -- and not just because of the coal problem.
Interesting that on the whole, the same picture remained for rail passenger services after dieselisation. I was aware that CIE went diesel a while earlier than British Railways -- if I have things rightly, very little CIE steam working was left by the end of the 1950s, in just a very few spots. Had had the pic. that after the coal horrors of WW2 and aftermath, CIE's management had concluded that becoming reliant on a different sort of fuel, equally got totally from sources outside their island, could at least not be worse than the previous situation (they'd given a good try, to turf as a fuel for steam locos, and concluded that it just could not be efficient in that capacity).
I recall mentions-in-passing in Bryan Morgan's The End Of The Line -- which I know I tend to regard as "Holy Writ" in matters of this kind -- referring to the then Irish transport situation (I have the impression that Morgan liked Ireland just fine, but didn't have a lot of use for its railways): he expresses fears re his beloved France showing, in the early 1950s, a strong tendency toward ongoing lessening of public passenger services -- rail and road -- country-wide, so as to threaten to make such facilities or lack thereof, as bad as was the case in the Irish Republic.
Ireland of course, has had the additional oddity that because of its partitioning, and how things were implemented re same: with the Great Southern involving only undertakings "south of the border", all railway undertakings totally in the Six Counties, or with sections either side of the border, continued "as they had been" -- a scene comparable to that of pre-Grouping Great Britain, continuing in a several decades' "time-warp". With things thus -- largely because of the existence and geography of the Great Northern Railway of Ireland -- for a long while, some two-fifths of the island as a whole, was rail-served not by the GSR and subsequently CIE. Am I right in reckoning that these, other, systems, had throughout better and more frequent passenger services, than "further south and west"? (I'm aware that the Ulster Transport Authority, quite shortly after its formation in 1949, carried out a closure-holocaust of pretty well all its lesser lines; but one envisages the UTA maintaining a decent service on the parts which it did keep on.)