Really good point. Travelling around Ireland - outside of the Dublin to Cork/Limerick/Galway corridors - without a car is not impossible, but it isn't easy.
Comparatively, doing so on the big island is easier. Certainly, it is in Switzerland. Or Germany, despite the size of the country.
I do agree, but the caveat with Switzerland is always money. They have lots of it. Just a hypothesis, but there is a lot more money sloshing around in Switzerland to invest in such sites. The locals have a lot more disposable income. Then there are lots of tourists. Normally, wealthy tourists with lots to spend. Add all of these factors together and it's no wonder the country can support more 'non essential' things like heritage railways.
On a related point, a lot of heritage railways in Britain benefit from charity status. I feel uncomfortable about that (although not a downright hostile as I am am to posho private schools doing so). In the awful world in which we current live, I personally think there are better 'charities' to support than old bearded white men playing with trains (that's obviously exaggerated and slighted tongue in cheek, but does broadly represent my discomfort).
All in, I come back to the point that we need to get behind the few sites and operations we have. Quality over quantity is the key for me.
As always, just my opinions, which are there to be blown out of the water....
David