Was thinking about this the other day, when preparing some notes for a magazine article and the answer is not easy to fathom, other than the obvious delights and the fact that it makes a very satisfying alternative to the conventional 'terminus-fiddle yard' concept.
I started off in 4mm scale, EM gauge, modelling Light Railway practice. The Colonel Stephen's railways have always fascinated me & we do share a name [my surname, being his Christian one]. After a couple of layouts, one of which was exhibited in the late 80s [Oare], I turned to 7mm NG, mainly because I liked the chunkiness of the larger scale. I also had lots of spares, particularly wheels, in 00 and found that I could build freelance locos on commercial chassis that were visually satisfying and also worked well. When the Hornby 08 shunter came out, the outside cranks made for an ideal base for a NG diesel and it was quickly chopped up and re-vamped the way some of you create Irish prototypes. Lima 08s and 2-6-2T chassis got similar treatment and the High Weald Light Railway appeared in RM in the early 90s. It was followed later by Cranbrook Town, which also got an article, along with several others on various locos and buildings.
Loose End came next, also in RM, a layout I look back on fondly, because it ran well, looked good and introduced me to Gordon & Maggie Gravett, who remain good friends. Bizarrely, after I sold it to a chap near Nottingham, it then ended up in France, in the same barn where the Gravett's Ditchling Green resides. Strange or what? Loose End was a standard gauge, roadside tramway, based on the Wantage. Did my first proper scratch build for it, with the MRJournal's multi part article on how to do it from Laurie Griffin. Gave me the confidence to do a D16 Claud Hamilton after that, then a B17 footballer, so guess loco building fears were largely conquered by them - though I still get things wrong!
the mainline locos were built to get a mainline layout out of my system and now my local club are doing a 7mm oval, I feel I have exorcised that particular ghost and find myself far happier with something more manageable in Arigna Town. As to why Irish - can only re-iterate the charm, and the fact that it something a bit different. That and [on the minor lines at least], the similarities to the col stephens lines. Which is where I came in...